Heat a grill pan or basket over medium-high heat. Coat pan with cooking spray. Remove chicken from bag; discard marinade. Sprinkle chicken evenly with salt and black pepper. Add chicken to pan; cook for 2 minutes on each side or until done. Remove chicken from pan; keep warm. Remove onion and bell peppers from bag, and discard marinade. Add onion mixture to pan; cook for 6 minutes or until tender, turning after 3 minutes. Toast tortillas in pan, if desired. Place 2 tortillas on each of 4 plates, and divide chicken mixture evenly among tortillas. Divide onion mixture evenly among servings. Garnish with jalapeño slices. Serve with salsa, sour cream, and cilantro, if desired.