Cut peeled eggs lengthways into halves. Carefully remove yolks and set whites aside. In a small mixing bowl mash yolks and blend in sour cream, mustard and salt. Fill whites with this yolk mixture. In a large iron skillet melt butter until bubbling. Saut? green bell pepper, red bell pepper and onion in butter until they just become tender (do not over-saut?'). Remove from heat and stir in soup and sour cream. Spread one-half the soup/sour cream mixture in the shallow baking dish (about 1-1/2 quart) and add eggs (cut side up) in single layer (the mixture, if thick enough, will help somewhat keep the eggs from overturning, but if some do, don't worry about it). Carefully pour remaining soup mixture over top. Sprinkle with cheddar cheese and bake 20 minutes in oven at 350°F until heated thoroughly and cheese melts. Serves 6 to 8.