Salt and drain diced tomatoes in a colander for 5 minutes, then pat dry. This removes excess moisture and prevents a watery dip.
Combine drained tomatoes, garlic, basil, olive oil, balsamic, salt, pepper, and red pepper flakes in a bowl. Toss gently and taste for seasoning.
Refrigerate covered for at least 20 minutes before serving cold, or proceed to the hot version.
For hot version: spread softened cream cheese in an oven-safe dish. Top with half the mozzarella, the tomato mixture, remaining mozzarella, and Parmesan. Bake at 375°F for 18 to 22 minutes until bubbly and golden.
Toast baguette slices brushed with olive oil at 375°F for 8 to 10 minutes until crisp. Rub with a cut garlic clove while warm. Serve immediately with the dip.