Preheat the oven to 375°F (190°C). Lightly grease a 9x13-inch (23x33 cm) baking dish.
Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the Italian sausage and cook, breaking it apart with a spoon, until browned and cooked through. Confirm the sausage has reached an internal temperature of 160°F (71°C).
Add the diced zucchini, chopped mushrooms, minced garlic, Italian seasoning, and onion powder to the skillet. Cook, stirring occasionally, for 5 to 7 minutes, until the vegetables have softened.
Pour the marinara sauce and water into the skillet. Stir everything together and bring the sauce to a gentle simmer.
Spread 1 cup of the sauce evenly over the bottom of the prepared baking dish.
Arrange half of the frozen ravioli in a single layer on top of the sauce. Cover the ravioli with half of the remaining sauce, then sprinkle with half of the shredded mozzarella cheese.
Create a second layer with the remaining frozen ravioli, the rest of the sauce, and the remaining mozzarella cheese.
Cover the dish tightly with aluminum foil and bake for 60 minutes. The ravioli will cook through in the sauce.
Remove the foil and continue to bake for an additional 15 to 20 minutes, until the casserole is bubbling and the cheese is fully melted. Let the ravioli lasagna rest for 10 minutes before serving.