Preheat the oven to 450 degrees F (230 degrees C).

Cut baguette into 30 slices; brush slices with 2 tablespoons olive oil on both sides. Arrange on a baking sheet; sprinkle with salt.

Toast in the preheated oven until light golden brown and crisp, about 5 minutes.

Meanwhile, cut each tomato into 6 slices.

Flip bread slices; top each with 1 slice each tomato and mozzarella. Sprinkle with salt.

Bake in the preheated oven until tomato is warmed through and mozzarella is melted, about 5 minutes.

Transfer crostini to a serving platter; sprinkle with basil. Drizzle with remaining 2 tablespoons olive oil; sprinkle lightly with salt and black pepper.