In a skillet, melt butter over medium heat. Add the green pepper, onions and mushrooms; cook and stir until tender. Stir in peas, ham, mustard and salt; heat through. Gently stir in eggs; set aside. For sauce, melt the butter in a saucepan. Add flour, salt and pepper; stir to make a smooth paste. Add the milk all at once; cook and stir 1 minute more. Add ham mixture and heat through. Serve in pastry shells.