In the bowl of a stand mixer fitted with the flat beater attachment, combine the flour, salt, and black pepper. Add the cold butter and shortening, tossing briefly to coat them in the flour mixture.

Mix on medium-low speed until the mixture resembles coarse cornmeal, with butter pieces no larger than small peas. Add the ice water and mix on low speed just until the dough begins to come together.

Shape the dough into a flat disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Preheat the oven to 375°F (190°C). Roll the chilled dough on a lightly floured surface to a thickness of approximately ¼ inch. Transfer the dough to a 9-inch tart pan, pressing it gently into the fluted edges. Trim excess dough.

Line the tart shell with aluminum foil and fill with dried beans or pie weights. Bake for 25 minutes. Remove the foil and weights, then bake for an additional 5 minutes. Remove from the oven and allow the crust to cool to room temperature.

Using a mandoline or sharp knife, slice the squash, zucchini, and bell pepper into ⅛-inch rounds. Slice the red onion into thin half-moons.

Evenly sprinkle the goat cheese and basil over the cooled tart crust.

Arrange the vegetables in overlapping concentric circles, beginning at the outer edge of the tart and working toward the center. Drizzle evenly with olive oil and season lightly with salt and black pepper.

Bake the assembled tart for approximately 30 minutes, or until the crust is golden brown and the vegetables are tender.

Remove from the oven and allow to cool slightly before slicing and serving.