Preheat oven to 350°F. Place beef in medium skillet; sprinkle with black pepper. Add bell pepper and onion; cook 6 to 8 minutes over medium-high heat or until beef is crumbled and no longer pink, stirring occasionally; drain.
Stir in pasta sauce; bring to a simmer. Spoon 3/4 cup beef mixture across each tortilla, just below the center. Top beef mixture with one piece string cheese. Pull bottom of tortilla up over filling, fold over sides and roll into a burrito.
Place seam-side down on ungreased baking sheet. Bake 10 minutes or until lightly browned on top.