Preheat the oven to 350 degrees F.
Combine the tomatoes, breadcrumbs, garlic and 2 tablespoons of the olive oil in a bowl, and toss to coat. Spread on a sheet pan and bake until the tomatoes are softened and the breadcrumbs are toasted, about 15 minutes.
Meanwhile, brush the remaining 2 tablespoons olive oil onto the baguette slices, sprinkle with some kosher salt and pepper and top each with a slice of mozzarella. Place on a sheet pan and toast in the oven until golden brown and the cheese is melted, about 8 minutes.
Remove both the tomatoes and the bread from the oven and top each slice of cheesy bread with some tomatoes. Garnish with a sprinkle of smoked sea salt.