Cook onion and pepper in hot oil. Combine soup and milk and stir into vegetable mixture. Heat to boiling. Add ham and lemon juice. Pour into a 1 1/2 quart casserole.
Combine sweet potato and melted fat. Add beaten egg. Mix flour with salt and add to sweet potato mixture. Mix well. Spread over ham mixture in casserole.
Bake for 40 minutes, until top is browned and filling is bubbling.