Wash peppers and halve lengthwise, cleaning out seeds, and set aside. Combine ground beef, breadcrumbs, egg, seasonings and milk into a meatloaf-like mixture. Pack into pepper halves. Place in crockpot, stacking peppers in layers. Pour spaghetti sauce over top. Cook in crockpot on high for 4 hours, or on low from 6 to 8 hours.
Serves 6-8.