Preheat your oven to 375°F (190°C).
In a large skillet, heat olive oil over medium heat. Add diced onions and sauté until they become translucent, about 3-4 minutes.
Add minced garlic and cook for another 1-2 minutes, until fragrant.
Add ground beef to the skillet, breaking it apart with a spatula. Cook until browned and no longer pink, about 5-7 minutes.
Stir in Italian seasoning, salt, and pepper. Mix well and let cook for an additional 2 minutes to combine.
Move the beef mixture into a greased baking dish, spreading it evenly.
Slice zucchini into thin rounds and layer them evenly over the beef mixture.
Sprinkle shredded mozzarella cheese evenly on top.
Bake in the preheated oven for 25-30 minutes until zucchini is tender and cheese is bubbly and golden.
Remove from the oven and let it cool for 5-10 minutes before serving.