1. Drizzle lemon juice over avocado; toss gently to coat. Set aside.
2. Trim fat from steak. Cut steak into two 1-inch thin strips. On four 12-inch skewers thread steak, accordion-style. On four 12-inch skewers alternately thread onion and peppers. Brush vegetables with oil.
3. Grill the kabobs on the rack of an uncovered grill directly over medium heat for 10 to 12 minutes or until steak is cooked to desired doneness, turning kabobs once and brushing occasionally with picante sauce.
4. To serve, divide the steak, onion, peppers, avocado, and lettuce among the tortillas. Fold tortillas over filling. If desired, serve with additional picante sauce.