Heat a pan to medium high heat and add 1 tbsp oil. Add the sausages and cook until caramelised and golden on all sides. Meanwhile, heat 2 tbsp oil in a frying pan and cook the onions until soft and golden. Stir in the chilli sauce, tomato sauce and season to taste. Cook 2 mins until sticky.
Take the buns, add a spoonful of the sweet chilli onions, top with a sausage, then spoon over more onions.