Heat the olive oil in a small stockpot or Dutch oven set on high heat until sizzling, about 2 minutes. Add the sausage and cook for 3 minutes. Using a slotted spoon, remove the sausage to a bowl and set aside. Add the onions, garlic, red pepper flakes, salt, pepper and sun-dried tomatoes to the same pan and cook on medium-high heat for 3-5 minutes, stirring occasionally, until the onions are soft. Stir in the wine and cook for 1-2 minutes. Add the cabbage, the reserved cooked sausage and the chicken stock and bring to a boil. Reduce the heat to low and simmer with the lid slightly ajar for 10-15 minutes, until the cabbage is tender.
To serve, place a piece of the garlic toast in the bottom of a shallow soup bowl and ladle the soup over the top.