Combine the tomatoes, shallot and mozzarella with the 2 tablespoons olive oil, 1 tablespoon balsamic vinegar, 1 1/2 teaspoons flaky sea salt, 1/4 teaspoon freshly ground black pepper, and 1/4 teaspoon red pepper flakes. Gently toss until everything is mixed well. Let sit at room temperature for 15 minutes so the flavors can meld and combine.