Preheat oven to 400℉
Slice zucchini into thin slices. Line your baking pan with parchment paper and brush with olive oil. Then spread the zucchini slices on oiled parchment paper and sprinkle with salt and pepper. Roast about 5-8 minutes. Watch carefully so they do not brown.
Turn oven temperature down to 350℉
Add a little oil to your skillet and cook ground sausage for about 8-10 minutes. Crumble up the sausage with a spatula while it sautés. Spoon into a bowl and set aside.
Season ground beef with salt. Brown the beef in a pan, drain off about half the fat, and then add one cup of sauce, stir and let it simmer for a minute or two. Set aside.
Mix ricotta cheese, egg, parsley, 1/2 teaspoon of salt and 1/4 teaspoon of pepper in a bowl. Set aside.
Spoon sauce into the bottom of your casserole dish. Layer with zucchini strips, the ground beef mixture, one and a half cups of mozzarella cheese, zucchini strips, ricotta cheese mixture, sausage, one cup of sauce, and the remaining one and a half cups of mozzarella cheese.
Bake uncovered for 30-40 minutes. Let your casserole rest about 15 minutes before slicing and serve with extra sauce and grated parmesan cheese, if you like.