Saute diced zucchini in olive oil till tender, about 10 minutes.
Brown beef, then add in marinara and mix well.
Prepare topping by mixing together almond flour, parmesan, salt, pepper and garlic powder in a small bowl.
In a 9x13 inch baking dish, pour half the zucchini in the bottom of the dish, then pour half the marinara/meat mixture on top of zucchini and top with mozzarella.
Add the rest of the zucchini on top of mozzarella and then the rest of the marinara/meat mixture.
Top casserole with almond flour/parmesan mixture.
Bake at 350 degrees for 25 minutes, then turn oven to broil and broil for 2-3 minutes till topping gets crispy and golden brown.