Slice 4-5 tomatoes with skin on and place on paper towels to drain - about an hour or longer if you have time.
Heat oven to 400 degrees. Roll out pie dough and place in pie or tart pan and trim edges. Prick pie shell to prevent rising. Bake for 8 minutes, remove from oven and let cool for about 20 min.
Layer onion on bottom of pie shell then sprinkle on grated mozzarella and Parmesan cheese to form an even layer.
Spread pesto over cheeses.
Layer half the tomatoes over pesto in a circular pattern overlapping.
Mix mayo with grated cheddar cheese and spread on top of tomatoes.
Sprinkle on fresh basil.
Layer remaining tomatoes over basil.
Bake at 400 degrees for about 25 minutes minutes. If the edges get brown early, put a pie ring on top or use a homemade one made out of tinfoil.
Remove pie from oven and sprinkle on additional Parmesan cheese.
Allow pie to rest at least 30 minutes, sprinkle on basil, slice and serve.