1. In medium bowl, whisk together lime juice, 4 tablespoons oil, garlic, Worcestershire, brown sugar, jalapeño, cilantro, 1 teaspoon salt, and 3/4 teaspoon pepper. Reserve 1/4 cup marinade in small bowl; set aside. Add another teaspoon salt to remaining marinade. Place chicken in marinade; cover with plastic wrap and refrigerate 15 minutes. Brush both sides of onion rounds and peppers with remaining 2 tablespoons oil and season with salt and pepper.

2. Light all burners on gas grill and turn to high, cover, and heat grill until hot, about 15 minutes; scrape grill grate clean with grill brush. Leave one burner on high heat while turning remaining burners down to medium.

3. Remove chicken from marinade and place chicken smooth side down on hotter side of grill; discard remaining marinade. Place onion rounds and peppers (skin side down) on cooler side of grill. Cook (covered) chicken until well browned, 4 to 5 minutes; using tongs, flip chicken and continue grilling until chicken is no longer pink when cut into with paring knife or instant-read thermometer inserted into thickest part registers about 160°F, 4 to 5 minutes longer. Meanwhile, cook peppers until spottily charred and crisp-tender, 8 to 10 minutes, turning once or twice as needed; cook onions until tender and charred on both sides, 10 to 12 minutes, turning every 3 to 4 minutes. When chicken and vegetables are done, transfer to large plate; tent with foil to keep warm.

4. When grill is empty, set all burners to medium. Working in batches, if necessary, place tortillas in single layer on grate and grill until warm and lightly browned, about 20 seconds per side. As they are done, wrap tortillas in kitchen towel or large sheet of foil.

5. Separate onions into rings and place in medium bowl; slice bell peppers lengthwise into 1/4-inch strips and place in bowl with onions. Add 2 tablespoons reserved unused marinade to vegetables and toss well to combine. Slice chicken into 1/4-inch strips and toss with remaining 2 tablespoons reserved marinade in another bowl; arrange chicken and vegetables on large platter and serve with warmed tortillas.

Serves 4 to 6