1. Preheat your oven to 220°C (425°F).
2. Peel and dice the carrot (or other vegetable of your choice) into approximately 2 cm (3/4 inch) pieces or slice into rounds.
Cut the yellow onion in half, peel it, and thinly slice it.
Slice the mushrooms into approximately 0.5 cm (1/4 inch) slices.
Cut the mozzarella into pieces.
3. On a baking sheet, place your pie crust.
Arrange the vegetable pieces on the pie crust, forming a circle along the outer edge of the crust, about 5 to 7 cm (2 to 3 inches) wide (leave the center of the crust empty).
Add the onion, mushroom slices, and mozzarella. Season with salt and pepper.
Then, cut the center of the pie crust into 8 sections, like a camembert cheese. Fold the points of the pie crust towards the outside of the crown.
4. Bake for approximately 12 to 15 minutes, or until the crust is cooked and golden brown (check by lifting it gently).
Season the salad of your choice.