Trim ends off squash, and slice thinly, lengthwise. Reserve 1/2 teaspoon salt and use the rest to salt both sides of zucchini slices. Place in a colander set over the sink and let rest for 10-15 minutes.
Mix together ricotta, parmesan egg, reserved 1/2 teaspoon salt, basil, oregano, black pepper, and crushed red chile flakes.
Rinse off zucchini slices and pat dry.
Spread ½ cup pasta sauce on the bottom of an 11x-7.5-inch casserole dish. Arrange a layer of zucchini on top, cutting pieces to fit any gaps. If desired, add another layer alternating the pattern.
Spread on half the ricotta, then sprinkle on 3/4 cup mozzarella. Top with 3/4 cup pasta sauce. Repeat layers. You might not use all of the squash.
Top with tomato slices and remaining mozzarella cheese.
Bake for 45 minutes, until cheese is browned and sauce is bubbly. Let cool at least 10 minutes before serving.
Notes
The number of zucchini or squash you need will depend on the size.
If you don't have an 11x7.5-inch casserole, you can also use a square baking pan.