In a bowl, combine the tomatoes and the basil, season with a little salt and pepper, and stir to combine. Set aside while you are toasting the bread on the grill.
Drizzle the bread slices with a little EVOO and season with some salt and pepper. Place them on the grill until they're lightly marked and toasted on both sides. Remove the bread from the grill to a platter then spread each piece of bread with some of the mascarpone. Top with some of the tomato mixture.
Preheat grill medium-high.