In a small food processor blitz the butter, garlic, salt and parsley.
Preheat oven to 180°c
Divide the butter between the sliced baguette and place on a baking tray, place in the oven and bake until golden in colour and the butter starts to bubble.
In a large sauce pan, add 2 tbsp olive oil over a high heat. Once hot, add the red onion, stirring frequently to prevent them burning. Add the garlic for 1 minute. Now empty the pouch of mussels into the pan. Stir well and place a lid on the pan, shaking the pan occasionally. Cook for 5-6 minutes. Once cooked, add the parsley and serve with the garlic bread on the side.
Notes
Remember to discard any mussels that don't open after cooking.