Preheat the oven to 375 F. Line a large baking sheet with parchment paper, and set aside.
Slice the Roma tomatoes into about 1/2" slices, about 5 slices per tomato. Spread the tomato slices onto the baking sheet with parchment paper. Drizzle tomatoes with olive oil, then sprinkle with salt and pepper. Roast at 375 F for 25-30 minutes, until softened and slightly caramelized. Remove from the oven and allow to cool.
For the Crostini:
While the tomatoes are roasting, slice the baguette into 1/4"-1/2" thick slices to get about 18 slices. Lay the sliced baguette on a separate baking sheet. Drizzle with olive oil, and lightly sprinkle with salt and pepper. Bake at 375 F for 3-5 minutes until crisp, then remove from the oven and allow to cool as the tomatoes finish roasting.
To Build the Bruschetta:
Spread pesto onto each baguette slice, then top each with an oven-roasted tomato. Divide the mozzarella slices amongst the crostini.* Bake these at 375 for about 3-4 minutes until the mozzarella has melted.
Remove from the oven, and allow to cool slightly. Drizzle with balsamic glaze, and top with fresh basil leaves.
*Tear some mozzarella slices into halves for smaller baguette slices, if desired.