Preheat the oven to 350 degrees.
In a large skillet, heat the olive oil spray to medium heat. Add the onion, garlic, oregano, red pepper flakes and meat. Cook until the onion is translucent and the meat is cooked through, about 10 minutes. Finally, add the sauce to the meat mixture.
In a small bowl, combine the Ricotta cheese and the Parmesan cheese. Season with salt and pepper.
Using a large Pyrex 9x13 baking dish, spoon a small amount of sauce to cover the bottom. Add a layer of zucchini. Add another layer of the sauce (1/3), then half of the Ricotta cheese mixture.
Sprinkle half of the meat on top of the Ricotta cheese mixture. Place another layer of zucchini. Add another third of the sauce, and half of the Ricotta cheese mixture.
Sprinkle the rest of the meat. Finish with the last of the sauce. Sprinkle the Mozzarella cheese on top. Bake for about 30 minutes or until the cheese has melted and the zucchini looks cooked through.