Preheat oven to 350 degrees.
Place pie crust in pie plate.
Arrange onions in the bottom of the pie in a circular formation.
Then arrange sliced tomatoes, around in a circle, and some in the middle.
Add salt and pepper.
Combine mayonnaise, cheddar cheese and dried Italian seasonings in a small bowl.
Mix well and spoon over tomatoes, leaving about 1 inch gap in between mayo and the edge of the pie so you can still see the tomatoes.
Place sliced cheese on top of mayonnaise layer.
Bake for about 30 minutes, at 350 degrees, or until cheese is golden.