In a ziplock bag, sealed, shake the honey and the dijon together to combine. Spoon ¼ cup out into a small bowl, cover and set aside.
Butterfly the chicken by slicing horizontally down the thick side to fold open. Sprinkle the chicken with salt and pepper and toss in the bag, mixing to coat. Let flavors mingle in fridge for at least 1 hour.
In the meantime, cook the bacon pieces in a large skillet over medium heat until nice and crispy. With a slotted spoon, transfer bacon to paper towel lined plate to drain. Reserve bacon fat.
When cooled, toss the pepper jack cheese and bacon together in a small prep bowl.
Preheat the grill for 15 minutes on hot, clean the and prep the grate. Reduce heat to low on one side and keep at medium on the other burners to maintain about 350 degrees.
Push a toothpick horizontally through the onion to hold the rings together while cooking (best tip ever btw, Cook’s!). Brush with reserved bacon fat and place on cooler side of the grill.
Place chicken on hotter side of the grill and grill to get a nice char, about 5 minutes. Flip onion and chicken and baste chicken with remaining honey mustard mix. Cover and cook another 5 minutes.
Remove onion slices from grill and transfer chicken to cooler side. Carefully separate the onion rings and toss over chicken with bacon and cheese mix. Cover grill and let melt, about 2 minutes.
Transfer to cutting board and let rest, covered, for 5 to 10 minutes before serving.
Serve with lime wedges and fresh pico de gallo on top.