Put sausages in a plate going in the microwave and poke them. Cover with plastic wrap leaving an open corner to let escape the steam and cook at high power for about 5 minutes or until not pink inside. (you can do this step in advance, let cool and cover. They will be good until the next day in the fridge.). Cut in slices of 1 1/2 inches of thickness.
Meanwhile, in a bowl, mix oil, garlic, salt and pepper. On metal skewers or wood skewers previously soaked in water, thread sausages alternating with bread cubes and onions squares. Baste the skewers with the mixture of oil.
Set the barbecue to medium heat. Put the skewers on an oil grill. Close the cover and cook about 10 minutes or until sausages are grilled and onions are tender (flip the skewers 3 times during the cooking time).