Preheat your oven to 375°F (190°C).
Slice the zucchini in half lengthwise and use a spoon to scoop out some of the inside, creating a hollow bowl. Lightly salt the inside and place the zucchini halves in a baking dish.
In a skillet over medium heat, cook the ground beef or turkey until browned. Drain excess fat if necessary.
Stir in the marinara sauce, garlic powder, Italian seasoning, salt, and pepper. Allow to simmer for about 5 minutes.
Spoon the meat mixture into each zucchini bowl evenly.
Top each filled zucchini with the shredded mozzarella cheese, followed by the sliced pepperoni, bell peppers, and black olives.
Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes.
Remove the foil and bake for an additional 5 minutes or until the cheese is bubbly and slightly browned.
Once done, remove from the oven and let cool for a few minutes. Garnish with fresh basil leaves if desired.