Heat oven to 200C/fan 180C/ gas 6. Mix the beef with the chilli and some chopped coriander, then season well. Shape into four patties about 2.5cm thick. Chill until needed.
Keeping the tomatoes on the vine, put them in a roasting tin. Drizzle over 1 tbsp of olive oil and season. Roast for 12-15 mins until just soft.
Heat 1 tbsp of oil in a non-stick frying pan. Then cook burgers on each side for 4 mins for rare or 5 mins for medium. For the relish, mix 2 tbsp of olive oil, the lime juice and sweet chilli sauce, parsley, coriander leaves and red onion. To serve, place a burger on a muffin half, add a branch of tomatoes and top with red onion relish.