In a large skillet, cook the ground chicken and diced onion over medium heat until the chicken is fully cooked and the onion becomes soft, about 5-7 minutes.

Stir in the marinara sauce, basil pesto, salt, and pepper. Let this delightful mixture simmer for about 10 minutes.

Preheat your oven to 350°F (175°C).

Grease the brioche buns generously with garlic margarine or butter and place them on a baking sheet.

Spoon generous amounts of the chicken mixture onto the bottom half of each brioche bun, then top with shredded Parmesan and mozzarella cheese.

Place the assembled buns in the oven and bake for 10 minutes or until the cheese is melted and bubbly.

Once out of the oven, pop on the top half of the buns and serve these scrumptious Sloppy Joes immediately.