Spread 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.