Preheat oven to 375°F. Line a rimmed baking sheet with foil and spray lightly with nonstick cooking spray.
In a medium bowl, mix together cheddar, pepper jack, cooked bacon, jalapeños, and green onions. Set aside.
Optional but recommended: sauté onion and bell pepper in a skillet over medium heat for 3–4 minutes. Add garlic for 30 seconds. Cool 5 minutes.
In a large bowl, combine ground beef, ground pork, eggs, breadcrumbs, milk, Worcestershire, barbecue sauce, mustard, and seasonings. Add cooled onion mixture (or raw onion if skipping the sauté). Mix gently just until combined.
Turn meat mixture onto the prepared pan. Pat into a 10×12-inch rectangle, about ¾-inch thick.
Spoon filling down the center, leaving a 1½-inch border around all edges. Fold meat over filling and pinch seams and ends closed. Smooth the top.
Whisk glaze ingredients together. Brush a thin layer over the top of the loaf.
Bake for 45 minutes. Remove and brush on more glaze.
Bake 15–25 minutes more, until the center reaches 160°F. Add extra cheddar on top during the last 5 minutes if desired.
Rest 10–15 minutes before slicing and serving.