HEAT oven to 250ºF.
SPREAD popcorn onto 2 rimmed baking sheets sprayed with cooking spray; sprinkle with bacon and nuts.
MICROWAVE caramels and milk in microwaveable bowl on HIGH 3 min. or until caramels are melted and sauce is well blended, stirring every minute. Drizzle over popcorn.
BAKE 45 min., stirring every 15 min. Remove from oven; stir. Cool completely in pans, stirring occasionally to break up large pieces.