Marinade chicken breast in balsamic vinegar overnight or for 1 hour before cooking.
Mix tomatoes, basil, olive oil, garlic and sea salt in a bowl and let sit at room temperature for an hour.
Pre-heat your Instant Pot using the Sauté function (normal), a cast iron pan on medium, or a grill.
Add a couple teaspoons of olive oil to your preheated pan.
Place chicken breasts in the pot and cook until edges are opaque, about 10 minutes. Flip to the other side, then cover the pot, and cook for another 10 minutes.
Serve chicken over a bed of spinach and top with the tomato mixture.