1. Drizzle lemon juice over avocado; toss gently to coat. Set aside.
2. Trim fat from steak. Cut steak into 3/4-inch pieces. On four 12-inch skewers, alternately thread steak pieces, onion wedges, and sweet pepper squares, leaving a 1/4-inch space between pieces. Brush vegetables with oil.
3. Place the kabobs on the rack of the grill directly over medium heat. Grill for 10 to 12 minutes or to desired doneness, turning kabobs once and brushing occasionally with the 1/2 cup picante sauce during the first half of grilling. Discard any remaining picante sauce used during grilling. Grill the tortillas directly over medium heat for 1 to 2 minutes or until lightly browned.
4. To serve, divide the steak, onion, and sweet peppers among the tortillas. Fold tortillas over filling. Serve with the avocado and lettuce. If desired, pass additional picante sauce, sour cream, and lime wedges. Makes 8 servings.
5. *Note: Use caution when handling hot chile peppers. Wear disposable gloves or wash hands thoroughly after preparation.