Whisk together olive oil, honey, Dijon mustard, salt, and pepper in a medium bowl until smooth. Transfer 1/4 cup of this marinade to a small container and refrigerate for later basting. Place the remaining marinade and chicken breasts in a large resealable bag, seal tightly, and massage gently to coat. Refrigerate for at least 30 minutes, though 1 hour gives better flavor.

About 25-30 minutes before grilling (during the last part of marinating time), cook bacon until crispy. For stovetop, cook over medium heat for 8-10 minutes, flipping occasionally. For oven, bake at 400°F for 20-25 minutes on a lined sheet pan. Transfer to paper towels, let cool for 5 minutes, then cut into bite-sized pieces.

Preheat grill to medium heat (350°F). Remove chicken from marinade, discard used marinade, and place chicken on grill. Cook for 6-9 minutes without moving until grill marks form.

Flip chicken using tongs and brush with the clean reserved marinade. Continue grilling for 6-9 minutes until an instant-read thermometer reads 162°F in the thickest part.

Brush the top surface with BBQ sauce and sprinkle with cheddar cheese. Close grill lid and cook for 3-5 minutes until cheese melts and bubbles. Watch closely to prevent burning.

Remove from grill and let rest for 3-4 minutes. Top with crispy bacon, fresh cilantro, and optional red onion or pickled jalapeños before serving.