Prepare Avocado Picadillo; cover and chill.
Rub both sides of meat with fajita seasoning; place in a large zip-top plastic bag, and marinate in refrigerator at least 8 hours.
Place peppers in a zip-top plastic bag. Stir together lime juice and next 3 ingredients; pour over peppers. Marinate in refrigerator at least 2 hours.
Place meat and peppers (skin sides down) on grill rack coated with cooking spray; grill, covered, 12 minutes. Remove peppers, and place in a zip-top plastic bag 10 minutes. Turn meat, and grill 10 minutes or until desired degree of doneness. Let stand 5 minutes. Cut meat diagonally across grain into thin slices. Remove skins from peppers, and cut peppers into strips.
Heat oil in a large nonstick skillet over medium heat. Add onion; sauté 15 minutes or until lightly browned.
Heat tortillas according to package directions.
Divide meat and vegetables evenly among tortillas. Top each tortilla with 1 tablespoon sour cream, 2 1/2 tablespoons Avocado Picadillo, and 2 tablespoons cheese; roll up.