Step 1Place tomatoes, oil, vinegar, salt and pepper to taste in bowl. Toss to mix well. Let rest at room temperature 2 to 3 hours before serving.
Step 2Lightly grill or broil 1 side of baguette slices. While still warm, rub grilled side with cut garlic. (Can be done a few hours ahead. Cover with foil; let rest at room temperature.)
Step 3To serve, stir tomatoes. Taste and adjust seasoning. Using slotted spoon to drain excess liquid, mound tomatoes on bread, dividing evenly. Place on platter, alternating with Umbrian Fried Flat Bread With Prosciutto; serve immediately.