Pour 1 tablespoon of olive oil into a small bowl and place the crushed walnuts onto a plate.
With each slice of mozzarella, dip and turn the edges into the olive oil, and then dab and roll the edges into the crushed walnuts to crust the edges of the mozzarella.
When ready to assemble the dish, the order I like to use is tomato, followed by mozzarella, followed by basil. Repeat until you've used everything.
Drizzle with the balsamic vinegar and garnish with some of the remaining basil.