In a mixing bowl, combine the diced tomatoes, red onion, basil, minced garlic, balsamic vinegar, olive oil, salt, and pepper. Mix well and let sit for 10 minutes to allow the flavors to meld.

In another bowl, beat the softened cream cheese until smooth. Stir in the mozzarella and Parmesan cheeses until well combined.

Add the tomato mixture to the cheese mixture and gently fold until just combined. If desired, add red pepper flakes for a bit of heat.

Transfer the bruschetta dip to a serving dish and refrigerate for at least 30 minutes before serving to enhance the flavors.

Serve chilled or at room temperature with sliced baguette or crackers.