Combine first 6 ingredients and, if desired, chipotle seasoning.
Stir together chili powder mixture and dressing. Pour half of marinade in a shallow dish or large heavy-duty zip-top plastic bag; add chicken. Cover or seal. Pour remaining marinade in a separate shallow dish or large heavy-duty zip-top plastic bag; add beef. Cover or seal; chill chicken and beef 2 hours.
Remove chicken and beef from marinade, discarding marinade.
Grill, covered with grill lid, over medium heat (300° to 350°) about 15 minutes on each side or until chicken is done and beef is at desired degree of doneness. Cut chicken and beef into strips. Serve in flour tortillas with desired toppings.