Heat a large frying pan over medium heat and brown the boerewors on all sides. Remove and set aside.
Add the oil to the same pan and fry the onions until soft and lightly caramelised.
Add the garlic and green pepper and cook for 2–3 minutes.
Stir in the chopped tomatoes, tomato paste, sugar, paprika, thyme, and water or stock.
Season with salt and pepper.
Return the boerewors to the pan, nestling it into the sauce.
Cover and simmer gently for 25–30 minutes, turning the wors occasionally, until cooked through and the sauce has thickened.
Serve the wors whole or sliced into pieces with plenty of the tomato and onion sauce.