1. Halve the avocado, remove the pip and peel and cut the flesh into cubes. Place the avocado in a bowl and dress with the olive oil, lemon juice, a pinch of salt and a generous sprinkling of black pepper.
2. Wash and cut the fennel into small pieces and add to the avocado. Add the well-drained, flaked tuna and mix gently.
3. Arrange the tartare on four individual plates, using a metal disc, if you have one, to form a patty shape, and garnish with a few salad leaves.
