In a skillet over medium heat, brown the steak in oil. Place steak
and drippings in a slow cooker. Add lemon juice, garlic, cumin, salt,
chili powder and red pepper flakes; mix well.
Cover and cook on HIGH for 2 1/2 to 3 hours or until meat is tender.
Add green pepper and onion; cover and cook for 1 hour or until vegetables
Warm tortillas according to package directions; spoon beef and vegetables
down the center of tortillas. Top each with cheese, salsa, sour
cream, lettuce and tomatoes, if desired. Fold in sides of tortillas
and serve immediately.