Healthy burgers

Name: Healthy burgers
Prep time: 25 min
Cook time: 40 min
Total time: 1 h 5 min
Cuisine: British
Ingredients: 400g lean beef mince (10% fat), preferably organic; 5 spring onions finely chopped; 140g finely grated carrot; 2 garlic cloves finely chopped; 2 tsp Dijon mustard; 1 tbsp chopped tarragon; 1 medium egg beaten; 4 wholemeal bread rolls, split in half; 1½ tsp rapeseed oil for brushing; 25g watercress; 2 large red peppers halved lengthways and deseeded; 100g cherry or baby plum tomatoes halved; 2 tsp lime juice; 2 tsp snipped chives; ¼ very small red onion thinly sliced; pinch crushed chillies