In a bowl beat eggs and salt together. In a 10-inch skillet melt the 2 tablespoons margarine or butter over medium heat. Pour in egg mixture. Cook, without stirring until mixture begins to set on the bottom and around the edges. Using a large spoon or spatula, lift and fold partially cooked eggs so uncooked portion flows underneath. Continue cooking over medium heat about 4 minutes total or until eggs are cooked throughout but are still glossy and moist. Immediately remove eggs from heat; set aside.
For sauce, in a 4-quart Dutch oven melt the 3 tablespoons margarine or butter. Stir in flour and pepper. Add milk all at once. Cook and stir until mixture is thickened and bubbly. Add the 6 ounces cheese and mustard, stirring until cheese melts.
Stir in vegetables and ham, then gently fold in eggs. Turn mixture into a 2-quart rectangular baking dish. Cover and chill for 2 to 24 hours.
Before serving, cover and bake in a 350 degree F oven for 45 minutes or until heated through, gently stirring after 15 minutes. After baking, gently stir again. Sprinkle with remaining cheese. Makes 12 servings.