Heat oven to 425°F. Spray 13x9-inch pan with cooking spray. Unroll dough; place in greased pan. Starting at center, press out dough with hands over bottom and 1 1/2 inches up sides.
Place string cheese, end to end, around edge of dough, cutting to fit if necessary. Reserve any remaining cheese. Fold edge of dough over cheese; pinch to seal under cheese. Bake 10 minutes.
Meanwhile, spray 10-inch skillet with cooking spray; heat over medium-high heat. Add onions and bell pepper; cook 5 to 7 minutes, stirring occasionally, until tender.
Add beans, tomatoes, tomato paste and corn; mix well. Heat to boiling. Reduce heat to medium; cook 6 to 8 minutes or until slightly thickened.
Reduce oven temperature to 375°F. Spoon bean mixture evenly into partially baked crust. Chop any reserved string cheese. Sprinkle with string cheese and Cheddar cheese.
Bake at 375°F 15 to 25 minutes or until crust is deep golden brown and cheese is melted. Let stand 3 to 5 minutes before serving.