Preheat grill to high. Brush tomatoes with oil and season with salt and pepper. Place on the grill and grill until charred on all sides. Coarsely chop the tomatoes and then place in a food process with the garlic, 1/4 cup of the olive oil, and the pine nuts. Process until smooth. Transfer to a bowl, stir in the thyme, and season with salt and pepper, to taste. Let stand at room temperature for 30 minutes.
Brush each slice of bread with the remaining oil on both sides, season with salt and pepper, and grill until lightly golden brown, about 30 seconds on each side. Remove the bread from the grill, brush 1 side of each slice with the pureed tomato mixture, and top each with a slice of prosciutto. Serve.