1. Combine first 6 ingredients, stirring well. Place chicken in a zip-top plastic bag. Add 3/4 cup beer mixture to bag; seal. Reserve remaining beer mixture. Marinate in refrigerator for 1 hour, turning occasionally. Combine onion, bell peppers, and remaining beer mixture in a zip-top plastic bag, and seal. Marinate for 1 hour at room temperature.
2. Heat a grill pan 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.