Preheat oven to 325F (163C)—line sheet pan with parchment paper. On a sheet pan, toss together tomato halves, oil, salt and pepper. Spread into an even layer and bake until shrivelled, about an hour. Let cool.
Onto baguette slices, arrange two bocconcini halves four roasted tomatoes, drizzle with balsamic and top with sliced basil. Drizzle with olive oil and sprinkle with additional salt and pepper, if desired.