There are few ingredients in this toast, barely touched, so every one of them matters and should be the best you can find. Be sure the avocado is just this side of soft here, so that it just barely gives when squeezed.
Squeeze the lemon juice over the slices of avocado, then lay the slices of avocado over the hot toast (nope, don't need butter). Drizzle tahini generously over the avocado and the toast. Top with the salt and sesame seeds. Eat immediately, then repeat.