Prepare mostaccioli as directed on package, rinse and drain, set aside.
In 2-quart souffle dish or 2-quart casserole, microwave margarine at high for 45 seconds or until melted. Stir in flour, basil, salt and pepper. Blend in milk. Microwave at high for 6 to 10 minutes, or until mixture thickens and bubbles, stirring with whisk every 2 minutes.
Stir in 1 cup Cheddar cheese, monterey jack cheese, and 1/4 cup Parmesan cheese. Stir to melt. Stir in cooked mostaccioli.
Arrange tomato slices on top of pasta mixture, if using. Sprinkle with remaining cheeses.
Bake for 30 to 35 minutes or until bubbly and lightly browned around edges.