Prepare crust according to package directions. In a saucepan over medium heat, brown beef and onion; drain. Add sloppy joe sauce; bring to a boil. Reduce heat; simmer, uncovered, for 5 minutes. On a floured surface, knead dough several times; pat into a greased 12- to 14- in. pizza pan. Bake at 425° for 10 minutes. Spread with meat mixture; sprinkle with cheeses. Return to the oven for 8 minutes or until the crust is brown and cheese is melted.