Preheat your oven to 375°F (190°C).
In a mixing bowl, combine the cooked chicken, diced bell peppers, diced onions, and olives. Mix well.
Add the marinara sauce, Italian seasoning, salt, and pepper to the bowl. Stir until all ingredients are evenly coated.
In a baking dish, spread the mixture evenly.
Top with shredded cheese, creating a nice, even layer over the top.
Bake in the preheated oven for about 20-25 minutes, or until the cheese is bubbly and golden.
Once done, remove from the oven and let it cool slightly before garnishing with fresh basil leaves.
Serve warm and enjoy your delicious crustless pizza bowl!