Slice your mozzarella and tomatoes, then just start layering them across your plate on top of the spinach. Mozzarella slice, basil leaf, tomato slice, repeat until the entire plate is covered.
Drizzle your salad with olive oil and balsamic vinegar, then add Kosher salt and pepper to taste.
I like to let mine chill in the refrigerator for an hour or so before serving, but you can also serve immediately for a prettier presentation.