Fire up your Pit Boss KC Combo and preheat both grill and griddle to 375°F. If using a gas or charcoal grill, set heat to medium heat. For all other grills, preheat cast iron skillet on grill grates.
Heat olive oil and butter on griddle, then add mushrooms and cook for about 3 minutes, stirring frequently. Add chopped onion and garlic and cook for 2 minutes. Add spinach and sauté another minute, then transfer vegetables to a heat-safe bowl to cool slightly.
Season the butterflied chicken breasts with Pit Boss Smoked Salt & Pepper Rub, coating both sides. Sprinkle half of cheese over each butterflied chicken breast, followed by the sautéed vegetables, and the remaining half of the cheese.
On a metal sheet tray, lay out two bacon slices. Gently fold chicken breast halves together and place on top of bacon slices, then wrap tightly with bacon. To secure, tuck ends of bacon underneath, or insert a toothpick to hold it together. Repeat with remaining breasts.
Arrange the chicken breasts, bacon seam down, directly on the grill grate and grill, turning once or twice, until the bacon is crisp and golden brown, about 25 to 30 minutes, or until internal temperature reaches 165°F.
Remove from grill, allow to rest for 5 minutes, remove any toothpicks, then serve hot.