Brown ground beef in medium skillet.
Add onions; cook until tender.
Season with salt and pepper to taste.
Sprinkle 2 tablespoons cheese onto each of four tortillas; cover with ground beef mixture, pepper strips, cilantro and remaining cheese.
Top with remaining tortillas.
Cook, in batches, in nonstick skillet over medium heat about 4 minutes or until cheese is melted, carefully turning after 2 minutes.