Heat oven to 375. Spray 13" x 9" pan with cooking spray.
Cook bacon till crisp; remove to paper towels to drain. Reserve 2 Tbsp drippings
In large glass vegetable cooking dish, stir together mashed potatoes, 2 Tbsp bacon drippings, milk, Jack cheese, cream cheese, pepper, and 2 c cheddar.
Microwave on High 4 minutes.
Stir in sour cream and drained chiles.
Spoon potato mixture into bottom of prepared pan.
Sprinkle with bacon and remaining 1 c cheddar.
Spoon meat evenly over cheese. Drizzle with barbecue sauce.