Wash and dry peppers well or they will splatter when you fry them. Cut the tops and bottoms off the peppers. Remove seeds and viens. Cut the peppers in half and then in half again.
In a large cast iron skillet, over a medium flame, add the oil. When oil is hot, add peppers and onions. I usually cover the peppers with a splatter screen so I don't make a mess of my stove. cook peppers until they begin to get blistered and a start to blacken. Remove from pan and drain on a paper towel.
Meanwhile, prepare sausage by removing the casings and breaking the sausage into pieces. Place sausage in a medium size skillet with a tight fitting lid. Begin to frying the sausage. Add 3/4 cup of water to sausage. Cover and cook until water is absorbed about 10 minutes. Remove lid and cook another 5 minutes to brown the sausage.
Cut the baquette in half and slice each half down the middle. Fill with peppers and sausage. Top with mozzarella cheese. Place sandwiches on a oven proof pan, placing rolled up foil in between to keep the sandwiches cheese side up. Heat under the broiler for about 1 minute to melt the cheese. You are going to love this sausage and peppers recipe!