BACON JAM: Cut bacon in 1-inch pieces. Fry in large skillet over medium heat until crisp (don't over cook). Drain on paper towels. Discard all but 2 Tbsp. bacon grease. NOTE: I keep my bacon grease in the fridge for other recipes.
Sauté onion, garlic and pepper in reserved bacon grease over a medium heat for about 4 to 5 minutes or until vegetables are tender. Return bacon to pan; add remaining ingredients. Bring to a simmer, reduce heat and continue to simmer for about 20 minutes or until thickened.
SANDWICH: Heat griddle over medium heat.
Butter the outer sides of bread; place on griddle. Spread mustard on inside of each piece of bread, layer each piece with a slice of cheddar cheese, and then add layer of chicken on one piece, top chicken with bacon jam and then place 2nd cheese, bacon slices and bread on top. Brown on each side, flipping occasionally to ensure cheese melts and that you don’t burn bread.