Preheat the oven to 190C/375F/Gas 5. Put the chillies, garlic, ginger, cumin and coriander seeds in a food processor with the coriander leaves, four tablespoons of the oil and some salt and pepper. Whizz to a paste.
Sit the chicken on a board and starting at the neck end, carefully slide your fingers between the skin and breast meat, so that the skin covering all the breast meat has been loosened. Push the coriander paste between the skin and the breast meat, spreading it out so that it covers the whole area. Smooth the skin back over the breast meat and tuck the ends underneath the chicken to secure it.
Sit the chicken in a roasting tin and drizzle over the remaining olive oil.
Season with salt and freshly ground black pepper and roast for 20 minutes per pound, plus an extra 20 minutes. Let the chicken rest for 10-15 minutes, then carve and serve with roast potatoes and steamed green vegetables, or salad leaves and crusty bread.