Method

• 1.
  Heat a large saucepan with a fitted lid over high heat. When hot, add mussels and 100ml water, then cover and cook, shaking the pan, for 1-2 minutes to heat through. Uncover and, using tongs, transfer mussels to bowl, discarding any that remain closed. Toss through lemon juice and chill for 30 minutes to pickle slightly.
• 2.
  Meanwhile, stand onion in a bowl of iced water for 10 minutes to soften flavour, then drain.
• 3.
  Drain mussels, reserving 2 tsp cooking liquid. Return to bowl and toss through the coriander, parsley and reserved cooking liquid.
• 4.
  Toast sourdough and rub with cut side of garlic while hot.
• 5.
  Gently toss onion through mussel mixture and divide among sourdough.
• 6.
  Scatter with smoked paprika and extra coriander and parsley, and drizzle with oil to serve.