HEAT oven to 375ºF.
COMBINE tomatoes, 3/4 cup barbecue sauce and onion powder in slow cooker; cover with lid. Cook on HIGH until ready to add meatballs.
MEANWHILE, cover 2 rimmed baking sheets with foil; spray with cooking spray. Mix meat, eggs, cracker crumbs, cheese and remaining barbecue sauce. Shape into 72 small meatballs, using about 1 Tbsp. meat mixture for each. Place on prepared baking sheets. Bake 15 min. or until done.
ADD meatballs to slow cooker; stir to evenly coat with sauce. Reduce heat to LOW to keep meatballs warm until ready to serve right from slow cooker.