Put cold water in the sink or a wash bowl, put the mussels in and clean. Cut the onions into bite-sized pieces and the peppers into strips.
Heat the oil in a large saucepan, fry the onions briefly and deglaze more or less with the wine, depending on your taste. Add the peeled canned tomatoes to the pot and cut into small pieces with a wooden spoon. Add the pepper strips and stock and simmer on medium heat.
After about 10 minutes, put the mussels in the pan, stir and cook for about 15 minutes until the mussels have opened. Please do not eat mussels that have not opened after cooking.