Preheat oven to 400°F. Line a rimmed sheet pan with parchment paper.
Roll the puff pastry to roughly 10×14 inches. Transfer to the pan and prick all over with a fork.
Stir ricotta with half the Parmesan, a pinch of salt and pepper, and a little thyme. Set aside.
Whisk Dijon and tomato paste until smooth and spreadable.
Toss eggplant, zucchini, squash, bell pepper, tomatoes, and onion with olive oil, garlic, remaining thyme, salt, pepper, and red pepper flakes.
Spread the mustard mixture over the pastry, leaving a 1-inch border. Spoon and smooth the ricotta mixture over it.
Arrange vegetables in alternating layers on top, slightly overlapping. Fold edges to form a rim.
Brush the crust with a little olive oil and sprinkle the remaining Parmesan over the tart.
Bake 35–40 minutes until crust is deeply golden and vegetables are tender. Cool 10 minutes, scatter basil, slice, and serve.
Notes
Variation: Swap ricotta with crumbled goat cheese for tang, or add a few sliced olives before baking. To store, refrigerate slices in an airtight container up to 3 days; reheat at 350°F until crisp.This recipe is an original creation inspired by classic Ratatouille Tart Recipe Delight flavors. All ingredient ratios and instructions are independently developed.