In a saucepan, heat 2 tablespoons of EVOO over medium-high heat. Add half of the onion, the garlic, tomato paste, and oregano, and season with a little salt and pepper. Cook, stirring frequently, for 2 to 3 minutes or until the onions soften. Add crushed tomatoes and bring to a boil. Lower heat to medium and cook for about 10 minutes, stirring every now and then until the sauce is thick.
For the burgers, combine the ground turkey or beef, sausage, pepperoni, green pepper, and the remaining onion in a mixing bowl. Add a little salt and pepper and mix with your hands until well-combined. Divide into 4 to 6 equal patties. Heat a large nonstick skillet over medium-high heat with 2 tablespoons EVOO. Add the burgers and cook on each side for 10 minutes or until cooked through. Once the burgers are cooked, top with smoked mozzarella, if using, and melt under the broiler.
While the burgers are cooking, cut the focaccia in half. Transfer the cooked burgers to the bottom triangles, top with some of the pizza sauce and then cover with the tops. Serve with a simple green salad.