Cook the spaghetti in boiling salted water
when cooked , drain reserving a good ladle of the water , toss in the olive oil and keep warm
Melt the butter in a large frying pan , add the onion and asparagus and sauté for 5 minutes
Add in the mussels garlic and chilli and cook for another 2-3 minutes
Stir through the parsley and chives. Season to taste
Add the spaghetti and some of the cooking liquid to create a sauce
Pour in the lemon juice , give a good stir
Serve immediately