Place a few tomatoes in the bottom of your clear plastic cup. Some people like to cut them in half, but sliced tomatoes create a lot of liquid in the cup if you are making this recipe the night before. I recommend you leave them whole.
Add a few each of the mozzarella squares and tortellini. The amounts are up to you.
Spoon a little of the pesto into the cup. Again, it's up to you how much. You can stir the pesto in with the other ingredients if you like. I did not as when you add the balsamic vinegar, the pesto will drizzle down.
If you decided to organize this caprese salad in a cup recipe the night before, then put the cups on a tray and cover with saran wrap. Place in the refrigerator overnight. You'll want to wait to add the balsamic vinegar until a few hours before serving.
When you are ready to add the balsamic vinegar, simply drizzle it over the top. I tend to add a little more as I love the flavor of balsamic vinegar and enjoy swirling the ingredients in it with my fancy bamboo toothpick.
And that's it - they are ready to serve!