In a large resealable plastic bag, combine the lime juice, cilantro, garlic and chili powder; add beef. Seal bag and turn to coat; refrigerate for 10 minutes, turning once.
Meanwhile, in a nonstick skillet, cook the peppers and onion in oil over medium-high heat for 5 minutes or until tender. Remove and keep warm. Add beef with marinade to the skillet; cook and stir for 4-5 minutes or until meat is tender and mixture comes to a boil. Add beans and pepper mixture; heat through.
Divide the salad greens among four bowls; top each with 1-1/4 cups beef mixture, 1 tablespoon sour cream and 1-1/2 teaspoons salsa.