Prepare the Sardines: place the drained sardines in a bowl. Add most of the chopped parsley, reserving some for the garnish. Add 1 tbsp of the lemon juice, a pinch of salt and a grind of pepper to taste. Combine everything using a fork to break up the sardines.
Prepare the Avocado: Scoop the flesh of half an avocado into a small bowl Add the chilli powder, 1 tbsp of lemon juice and a pinch of salt. Mash with a fork.
Toast the Bread: Toast the slice of sourdough bread until golden brown.
Rub the Toast with Garlic: Cut the end off the garlic clove and rub the cut end lightly over the surface of the warm toast. This will infuse the toast with a subtle garlic flavour. Drizzle the olive oil over the toast and place onto a serving plate.
Spread Avocado on Toast: Spread the mashed avocado evenly onto the toasted sourdough slices. Top with the sliced tomato.
Top with Sardines: Pile the sardines on top of the tomatoes.
Season and Garnish: Sprinkle the assembled dish with the reserved parsley and serve immediately with wedges of lemon.
