Sauté the whole sausages until browned on all sides and almost fully cooked (they will finish cooking after). Slice diagonally and transfer to a plate.

In the same skillet, sauté the peppers and onions in oil until slightly softened, then add garlic and rosemary.

Cook for another minute then add in the remaining ingredients along with the sausages. Reduce heat, cover and simmer until liquid is thickened and sausages are cooked throughout (if getting too thick, add a bit of water).