Put onions into a large skillet.
Pour bouillon over them and cover pan; simmer for about 5 minutes.
Add mushrooms and rhubarb sauce; sprinkle with sherry; then simmer for another 5 minutes.
In another skillet, fry sausage patties until done, pouring off grease as it accumulates.
Lay parties on top of onion mixture.
Sprinkle with cheese and top with walnuts.
Heat till piping hot (about 5 minutes) in a 350° oven.