In a heavy 3-quart saucepan cook bacon over medium heat until lightly browned, about 10 minutes. Do not drain fat.
Stir in the margarine and heat until melted. Add lettuce and saute for 2 minutes over medium heat. Whisk in the flour and heat stirring constantly until evenly cooked, about 3 minutes. Remove from heat and stir in the hot water, chicken soup base and tomato. Season with nutmeg and cayenne. Reheat the soup to boiling, stirring frequently. Reduce to a simmer and cook for about 6 minutes, stirring occasionally until thickened. Stir in the half and half and serve hot.