Preheat the oven to 375°F (190°C).
Heat 1 tablespoon of olive oil in a large skillet over medium heat.
Add the chopped onion and cook until softened, about 3 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet, breaking it apart with a spatula, and cook until browned and cooked through, about 7-8 minutes.
Drain any excess fat from the skillet.
Stir in the tomato sauce, dried oregano, dried basil, salt, and black pepper. Simmer for 5 minutes, then remove from heat.
Lightly grease a 9×13 inch casserole dish with the remaining 1 tablespoon of olive oil.
Arrange half of the zucchini slices in an even layer on the bottom of the casserole dish.
Spread half of the ground beef mixture evenly over the zucchini layer.
Arrange half of the tomato slices over the beef layer.
Repeat the layers with the remaining zucchini slices, ground beef mixture, and tomato slices.
Sprinkle the shredded mozzarella cheese evenly over the top layer.
Sprinkle the grated Parmesan cheese on top of the mozzarella.
Cover the casserole dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 10-15 minutes, until the cheese is melted and bubbly and the vegetables are tender.
Remove from the oven and let the casserole rest for 5 minutes before serving.