Place oil in a large skillet set over medium heat. Add onion, sweet pepper, eggplant and zucchini; cook until tender, about 5 min. Add pasta sauce, wine, sugar and 2 tbsp (30 mL) of cold water. Bring to a simmer; simmer for 5 min. Remove from heat and let cool to room temperature.
Bake tart shells as per package directions; let cool to room temperature.
Remove tarts from foil liners; place on a parchment paper–lined baking sheet. Divide ratatouille mixture among tarts; sprinkle with Parmesan cheese. Bake in a 350°F (180°C) oven for 10 min. or until filling is heated through.
To prepare these tarts in advance, bake the tart shells and make the filling up to 24 hours before you plan to serve them. Cool both to room temperature. Cover and store the filling in the fridge; cover and store the tart shells at room temperature. When ready to serve, fill and bake the tarts as described in step 3.