In a bowl, whisk together soy sauce, honey, garlic powder, smoked paprika, and black pepper for the marinade. Add the chicken breasts and marinate for at least 30 minutes (or up to 4 hours in the refrigerator).
While the chicken is marinating, prepare the honey mustard sauce by combining mayonnaise, Dijon mustard, honey, and apple cider vinegar in a small bowl. Stir until well combined. Set aside.
Preheat your grill or a grill pan to medium-high heat. Grill the marinated chicken breasts for about 5-6 minutes per side, or until cooked through and internal temperature reaches 165°F (74°C).
Once the chicken is cooked, place a slice of cheddar cheese on top of each chicken breast and let it melt for a minute. If using a grill pan, you can cover it briefly.
Lightly toast the brioche buns on the grill or in a toaster. Spread a generous amount of the honey mustard sauce on the bottom half of each bun.
Assemble the sandwiches: Place a grilled chicken breast with melted cheese on top of the sauce on each bottom bun. Top with crispy bacon, shredded lettuce, and a slice of tomato.
Place the top half of the bun on each sandwich. Serve immediately.
Notes
For a spicier kick, add a pinch of cayenne pepper to the marinade. You can also substitute the cheddar cheese with Monterey Jack or pepper jack for a different flavor profile.