Pound the chicken between sheets of parchment until evenly 1/2 inch thick.
Make the marinade by whisking olive oil, lime juice, mustard, garlic, paprika, cumin, chili powder, salt, and pepper.
Marinate the chicken for at least 30 minutes and up to 4 hours in the refrigerator.
Mix the sauce with mayonnaise, honey, Dijon mustard, and apple cider vinegar.
Grill the chicken for 5 to 7 minutes per side, or until the thickest part reaches 165°F.
Rest the chicken for 5 minutes while lightly toasting the buns.
Assemble the sandwiches with sauce, lettuce, chicken, tomato, and red onion.