Preheat oven to 350 degrees and spray a 9" square casserole dish with cooking spray. In a large mixing bowl beat the eggs, ricotta, Parmesan cheese, salt, pepper and Italian seasoning until completely combined.
Stir in sliced zucchini, diced tomatoes and well-drained spinach. When combined, transfer to prepared baking dish and bake for 1 hour or until the center is set and the casserole has browned slightly. Remove from oven and let cool on a rack for 10 minutes then slice and serve.
Notes
Use a larger pan for a shorter cook time, but a thinner casserole!