Cook sausage, onions, and, if desired, bell pepper, 2 teaspoons basil, and fennel seeds in a large skillet over medium-high heat about 10 minutes, stirring until sausage crumbles and is no longer pink and onions are tender. Drain.
Add flour, stirring until blended. Stir in tomato-and-basil sauce. Bring to a boil over medium-high heat, stirring constantly. Spoon mixture into a lightly greased 13- x 9-inch baking dish. Sprinkle mixture with 1 1/2 cups mozzarella cheese.
Unroll pizza crust, and place on top of sausage mixture. (Tuck edges into baking dish, if necessary.) Brush with olive oil, and sprinkle with remaining 1/2 cup mozzarella cheese, Parmesan cheese, and 1 teaspoon basil.
Bake at 425° for 20 minutes or until golden brown.