Finely chop the leeks keeping only the white parts and sautee them in a pan for about 15 minutes with 2 tbsp of olive oil.
Slice the zucchini, add 1 tbsp of oil and bake it for 15 minutes at 400 F heat.
At the same time, place the dough in a tart mold (8 inches), cover with parchment paper and top with beads for a bit of weight. Add it into the oven, side by side with the zucchinis. This will pre-bake the tart dough without burning it.
Remove the dough, beads and parchment paper on top. Spread the mustard onto the dough.
Add in the sauteed leeks, then the zucchini slices, tomatoes, 1 tbsp olive oil, and fresh thyme or herbs. Bake for another 15 minutes at 375 F.