Pre-heat oven to 350.
Spray 9×13 pan with cooking spray and set aside.
Heat oil in frying pan.
Place ground beef in pan and add garlic powder and Italian seasoning.
Cook until meat is crumbly.
Add marinara sauce and simmer until most of the liquid evaporates, about 10-15 minutes.
Combine 3 cheeses and stir in half of cheese mixture into beef mixture. Set aside.
Cut off zucchini stems and cut each zucchini in half lengthwise.
Using a melon baller scoop out insides of zucchini, save the insides for later uses.
Place Zucchini boats on to baking pan.
Spoon meat mixture into each boat making sure each boat is filled to the brim.
Sprinkle remaining cheese over each boat.
Bake in oven for about 30 minutes or until cheese has melted and started to turn brown.
Serve hot with salad or garlic bread.