In a large roasting or sheet pan, scatter half the onions. Rub the ribs with Cajun spices and overlap ribs onto the onions. Scatter remaining onions over the ribs. Pour a little water or stock into the pan. Cover tightly with foil and put into a preheated 350 degree oven, for 1 to 2 hours or until ribs are tender. When cooked, brush with barbecue sauce and grill or broil to glaze.