Another way to give moisture to the flan is to spread the base first with cream cheese, or melt this off in a pan and pour it over the veggies (or beat the egg into the melted cheese before pouring).
If no moisture is added, the contents of a flan could end up like 'roasted vegetables in pastry', although the thought has just come to mind that you could first fry off the veggies (or oven roast them) before using as a 'filling', and then put them in a pie dish with the pastry on top, tucking the edges down the side, then - after baking - turn out onto a plate to make an 'upside-down' flan - otherwise known as 'Tarte Tatin'.
A couple of recipes today might point you in the right direction, although you may wish to used different veggies/cheese, at least it gives an idea of how things go together.
Some recipes don't bake a pastry case blind when making a quiche, but myself always part blind-bake the case first as this prevents the base becoming soggy. The case can be baked earlier, paper and beans removed, then left - uncovered - at room temperature. This also gives the base a chance to dry out even more.
Another way to prevent 'soggy bottoms' is to paint a part-cooked base with egg (white, yolk or both) immediately it comes out of the oven and beans removed. The egg white cooks with the heat and makes a seal between the filling and the pastry.
As to whether the flan will freeze - this I'm not sure. 'Normal' quiches can be frozen, but myself never find this improves them. They keep fairly well in the fridge for several days, and then the amount needed is removed and brought back to room temperature before being eaten as the flavour tends to disappear the colder the food (this with almost any food). All I can suggest is when you make your flan, you cut a small wedge, wrap and seal and then freeze. Thaw it out a few days later and see how it turns out.
One of today's recipes does have freezing instructions.
A couple of recipes for a 'custard free' type of quiche/flan. It is not necessary to use the variety of cheese as given in the recipe, just take the details as a guide, and use the ingredients you have, nearest to the ones shown.
Two Cheese with Tomato Tart: serves 6 - 8
1 x 9" (23cm) pastry flan case, baked blind
1 tblsp Dijon mustard
6 ripe tomatoes, sliced
5 oz (150g) ripe Camembert cheese, sliced
5 oz (150g) soft goat's cheese, sliced
1 large egg plus one egg yolk
2 oz (50g/ml) creme fraiche
1 tblsp chopped fresh rosemary leaves
salt and pepper
Place the pastry case (it an still be in its tin) onto a baking sheet, then spread the mustard over the base of the cooked pastry case, then over with overlapping and alternating slices of the tomato and cheeses.
In a bowl put the whole egg, the egg yolk and the creme fraiche and whisk together. Fold in half the chopped rosemary leaves, season well (be generous with the pepper) and pour this evenly over the tomatoes and cheese. Sprinkle the remaining rosemary over the top.
Put the baking sheet into the oven (2ooC, 400F, gas 6) and bake for 40 minutes until just set and golden, then remove and allow to cool for 10 minutes before removing from the tin. Can be served warm or cold.
Freezing instructions are given: Cool completely, then wrap well in cling film followed by foil. Freeze for up to three months. Defrost thoroughly before serving cold, or cover and warm through in the oven.
The second recipe is more a tart than a flan, yet the 'filling' could still be baked in a short-pastry case rather than using puff pastry as in this instance. Again goat's cheese is used, but crumbled Mozzarella, Feta or even Wensleydale (at a pinch even grated Cheddar) should give almost the same effect (if not the flavour).
Note that these 'tarts' are made as individual servings, so double the ingredients if wishing to serve four (or just make one large one) and halve the amount if wishing to make just one for yourself.
If you haven't red pesto, then use green. If you haven't a jar of roasted red peppers in oil, then roast fresh bell peppers, remove skins and drizzle with oil. If you haven't thyme, use chopped rosemary leaves, or chopped parsley and mint.
Red Pepper and Goat's Cheese Tart: serves 2
375g pack of ready-rolled puff pastry
2 heaped tablespoons red pesto
1 x 290g jar of roasted red peppers in oil, drained
4 oz (100g) milk goat's cheese, cut into rounds
few sprigs fresh thyme
salt and pepper
Bring the puff pastry to room temperature before unrolling (otherwise it may crack). Cut in half and re-roll half back again and freeze for later use. Cut the reserved half into two equal oblongs and place onto a lightly greased baking tray.
Using the tip of a knife, scored a half-inch border around the edges of each pastry (but don't cut through), then divide and spread the pesto over each piece of pastry, keeping the pesto within the borders.
Cut the peppers into large chunks and lay these over the top, then place slices of the cheese on top of that, sprinkling over the thyme. Season to taste, then bake at 200C, 400F, gas 6 for 12 - 15 minutes or until the pastry is risen, golden and cooked through. Allow to cool for a couple of minutes before removing from tray and serving on plates.