Heat the olive oil in a large casserole dish. Add the courgette and sauté for 5 minutes until softened, then add the garlic and chilli flakes and cook for a further 2 minutes until fragrant.
Add the peas, watercress and vegetable stock, bring to a gentle simmer and cook for 10 minutes.
Remove from the heat and add the mint and parsley. Blend with a stick blender or heatproof blender until smooth. Stir through the butter until melted, then divide between two bowls.
Serve with a swirl of cream and a drizzle of olive oil.