Preheat the oven to 200°C conventional oven (400° Fahrenheit/Gas 6). Line a medium-sized baking tray with baking paper.
Scrub the mussels under cold running water to remove sand and barnacles. Discard any shells that are chipped, broken, or damaged in any way. Just before cooking, de-beard the mussels by holding a mussel between your thumb and forefinger. Using a paper towel to hold the beard and pull it downwards until it comes out and discard.
Heat 1 tablespoon (20ml) of extra virgin olive oil in a large saucepan over high heat. Add the whole garlic and cook without browning the garlic for approximately 1 minute. Add the mussels and cover. Cook for 5 minutes or until the mussels have opened.
Meanwhile to make the filling, place the breadcrumbs, crushed garlic, lemon zest, chopped parsley and capers into a mixing bowl. Add sea salt to taste and drizzle over the remaining 3 tablespoons (60ml) of extra virgin olive oil. Use a metal spoon to stir until well combined.
Pick up the mussels and separate the half empty shells from the half with the mussel. Discard the empty shells and arrange the half shell with the mussel closed together on the prepared baking tray. Place 1 teaspoon of the filling on each half shell, covering the mussel.
Bake for 10 minutes or until cooked through. Transfer half shells with mussels to a serving platter or individual plates. Serve with slices of lemon – buon appetito!