CUT thin slice off top of each pepper. Remove membranes and seeds; discard with tops. Combine meat, rice, peas and 1/2 cup cheese and 1/4 cup barbecue sauce; spoon into peppers. Top with remaining cheese.
POUR water and remaining barbecue sauce into slow cooker. Stand peppers, filled-sides up, in slow cooker; cover with lid. Cook on LOW 4 to 5 hours (or on HIGH 2-1/2 to 3-1/2 hours).
SERVE each pepper topped with 1 Tbsp. sauce.