Heat the butter and oil in a pan.
Sweat the onion until soft but not coloured. Add the garlic and cook for one minute.
Add the red pepper, chilli, tomato, courgette and wine and simmer until the wine has reduced to one tablespoon.
Add the mussels, cover the pan and simmer for five minutes or until the shells have opened. Discard any mussels that don't open during cooking.
Serve in a bowl and garnish with a sprig of chervil.