Pare, slice, and boil 2 medium-sized yams until tender. Drain and mash them and beat in a little warm milk until fluffy. (Canned, drained yams can be used instead.) Cook the green pepper in butter for about 8 minutes. Combine the soup and milk in a saucepan and add the onion, pepper, and mustard. Blend together the flour and water, add to the soup mixture, and stir over low heat until thickened. Add the green pepper and ham, and divide the mixture into six buttered ramekins. Top each with mashed yams and garnish with pieces of pineapple and marshmallow. Bake in a 350 degrees F oven for 20-25 minutes.