Add the Marsala or red wine if you are using, and with a wooden spoon scrape the bottom of the pan to release all the browned and blackened bits. Let the wine cook down by half. Add the tomatoes, oregano and red pepper flakes (if using) and stir well to combine. Add the sausages back in. Bring to a simmer then reduce the heat to low. Cover and simmer until the peppers are soft the sausages are cooked through, about 20 minutes. Sausage, peppers and onions will keep in the fridge for several days. Serve over polenta, or with penne pasta, or load up in a hoagie roll. Any leftover sauce makes a great sauce for pasta.