Preheat oven to 375 degrees.
Toss the onion slices with olive oil and season with salt and pepper.
Arrange the onion slices on the bottom of the pie crust.
Spread the cheese on top of the onions.
Layer on the basil leaves and arrange the tomato slices on top.
Sprinkle with Parmesan.
Bake for 45-60 minutes until crust is golden brown.
Cool slightly before slicing. Serve warm or at room temperature.