Prepare the vegetables for the topping of the pizza: cut the eggplant into 1/2-in chunks, sprinkle with salt and leave to drain for 15 minutes.
Rinse to remove the excess salt and pat dry with kitchen paper towels.
Cut the zucchini and red onion into 1/2-in chunks.
Halve the red and yellow bell peppers, remove the seeds carefully, cut into quarters and then into 1/2-in chunks.
Put the vegetables into a bowl, drizzle with oil and freshly ground black pepper.
Toss to coat.
Arrange the vegetables as a single layer on a baking sheet and roast in the oven for about 40 minutes until golden and crispy.
Sprinkle on a little salt towards the end of cooking.
Make the tomato fondue and cook it over a low heat until reduced and concentrated.
Adjust the seasoning if necessary.
Follow the recipe for gluten-free pizza base.
Roll out as two rounds and bake for 8 minutes.
Remove from the oven and spread the bases with the concentrated tomato fondue, then the roasted vegetables, and return to the oven for a further 10-15 minutes until hot, bubbly, and cooked through.