Spread the olive oil on the inside of a slow cooker. Place the venison roast inside, and cover with apple, onions, and garlic. Turn to Low, and cook until the roast is tender, about 6 to 8 hours.
When the roast has cooked, remove it from the slow cooker, and place onto a serving platter. Discard the apple. Stir the water and bouillon into the slow cooker until the bouillon has dissolved. Serve this as a sauce with the roast.