Combine sour cream and salsa in small bowl; mix well. Cover; refrigerate until serving.
Spray 10-inch skillet with no stick cooking spray; add onion and green pepper. Cook over medium heat, stirring occasionally, until vegetables are crisply tender (5 to 6 minutes). Stir in corn and roast beef. Continue cooking, stirring occasionally, until heated through.
Heat broiler. Spoon 1/6 corn mixture onto each pita bread; top with 2 slices cheese. Broil 5 to 7-inches from heat until cheese begins to melt (1 to 2 minutes).
Spoon 1 Tbsp sauce over melted cheese. Fold pita in half. Serve with remaining sauce.
Servings: 6