Cheese Fondue

1-1/2 cups margarine (I use a lot less - just enough to saute, not deep fry)
1/2 onion, chopped
Garlic salt
2 cans sliced mushrooms, chopped
1 lb Velveeta
2 cans mushroom soup

Saute together margarine, onion, garlic salt and mushrooms until onions are clear. While sauteing, chop Velveeta into smaller pieces and put into slow cooker. Add mushroom soup and sauteed mixture. Stir and cook until it's all melted together.