Melt butter in a medium saucepan over medium heat, then add in the onions. Once softened, reduce the heat to low and stir every 5 minutes so they don't burn. Cook at least 25 minutes, but up to 40 minutes for fully caramelized onions.
1 large onion, 2 tablespoon unsalted butter
Meanwhile, season both sides of the chicken cutlets with BBQ rub and then brush BBQ sauce on both sides. Preheat air fryer to 400 degrees and cook chicken for 15-18 minutes, until it reaches 165 degrees F.
2 chicken cutlets, 1 tablespoon BBQ rub, 2 tablespoon BBQ sauce
Cook bacon (microwave, oven or stovetop) and pat off excess grease. Break each piece in half.
2 slices bacon
Brush BBQ sauce on both sides of the burger buns and toast for 2-3 minutes. Then add a slice of cheddar to the top part of each bun and toast until cheese has melted.
2 burger buns, 2 slices cheddar cheese
Drain excess butter from caramelized onions.
Assemble the sandwich by placing the lettuce and tomato on the bottom part of the bun. Add the chicken cutlet, bacon pieces, caramelized onions and top of burger bun. Serve immediately.
2 slices tomato, 2 leaves lettuce