Prep the zucchini: Place the sliced zucchini in a colander and sprinkle lightly with salt. Toss to coat and let sit for 15 minutes to draw out moisture. Rinse under cold water and pat dry with paper towels.

Cook the beef mixture: In a large skillet over medium-high heat, warm the olive oil. Add the diced onion and sauté until softened, about 2 minutes. Stir in the garlic and ground beef. Cook, breaking the meat apart, until fully browned, about 5 minutes.

Season: Add the drained tomatoes, Italian seasoning, salt, and pepper. Stir to combine and remove from heat.

Assemble: Preheat oven to 350°F. In an 8×8-inch baking dish, spread half the beef mixture on the bottom. Layer with half the zucchini, then sprinkle with half the cheese. Repeat with the remaining beef, zucchini, and cheese.

Bake: Transfer to the oven and bake for 20–25 minutes, or until the cheese is melted and golden on top.

Rest and serve: Let the casserole sit for 10 minutes before slicing and serving.