Preheat your grill to medium-high. While heating, combine the ground turkey, turkey sausage, panko bread crumbs, ground basil, ground oregano, fennel seeds, garlic powder, kosher salt, ground black pepper, and crushed red pepper flakes in a large mixing bowl. Mix gently with your fingers, being careful not to compact the meat.
Shape the mixture into six patties and set aside. Place the patties on the hot grill and cook until browned on the bottom, about five minutes.
Flip the burgers and grill for another five minutes, adding slices of Mozzarella cheese and Asiago cheese just before they finish cooking.
In a medium bowl, toss the sliced red onion, green bell pepper, and red bell pepper with extra virgin olive oil, salt, and pepper. Grill in a basket until charred, about eight minutes.
Toast the wheat hamburger buns on the grill until golden brown.
Assemble the burgers by placing patties on buns and topping with the grilled veggies. Serve hot!
