Onion Bombs / Grill / The size of each meatball is going to depend on the onions. roll up the meatballs. Squish them between two pieces of onion.wrap them use one layer of regular foil and one heavy duty, twist top closed. they will be in the fire or hot coals. put in the hot coals. This could work on the grate or in smoker. Cook for about 8 to 10 minutes, flip them, flip again in 8 to 10 minutes (or so). leaving them a little longer would be ok as the onion keeps the meat juicy.