Preheat the oven to 250°C and roast the sausages for 5 minutes. Pan fry the onions, garlic, chilli and thyme in olive oil, until golden. Add rock salt to release the moisture from the onions. Add the tomatoes and chicken stock and bring to the boil. Once boiled, add the roasted sausages and mixed beans. Season with paprika, salt and black pepper. Transfer the mixture to the slow cooker and let it sit on medium heat for approximately 4-5 hours or until it thickens. In a separate bowl, mix the soy sauce with the vinegar and sugar. Take the casserole off the heat and add the soy sauce mixture, to give the casserole a sweet and sour flavouring. Finish with chopped fresh parsley.