In a medium skillet, heat the olive oil and sauté the garlic, mushrooms, and spinach. Season with salt and pepper. Once the spinach has wilted, set the mixture aside. This process takes about 5 minutes.
Slice the zucchini in half. Using a small, pointed spoon, scoop out the zucchini flesh.
In a medium mixing bowl, combine the ricotta cheese, parmesan cheese, ¼ cup mozzarella cheese, and sautéed vegetable mixture. Once combined, spoon the mixture into the hollowed-out zucchini.
Sprinkle the top of the zucchini with the remaining mozzarella.
Bake at 425 degrees for 20 minutes, or until the cheese on top has melted and is starting to turn a little brown.
Notes
These can also be cooked on the grill. Once the grill is hot, about 400 degrees, place the zucchini boats on the grill.