Slice the avocado lengthwise and extract the pit carefully. With a paring knife, score the avocado flesh into small cubes while still in its peel. Drizzle the flesh with freshly squeezed lemon juice and scatter a pinch of sea salt over it. Scoop out the diced avocado onto the prepared toast slices and gently mash it using the back of a fork. Finish by adding any toppings you prefer.