Heat the grill to high, or fire up your broiler and set the rack about 4-5 inches from the flames. Grill the bread slices until slightly charred on both sides. Cut into 1-inch cubes. Toss the asparagus with 3 tablespoons of the olive oil. Sprinkle with salt and pepper. Grill or broil for 3 to 5 minutes, until tender. Cut into 1-inch segments. Add the vinegar, garlic, 1/2 teaspoon salt, 1/4 teaspoon black pepper, and the rest of the oil in a large bowl. Whisk together until combined. Add the tomatoes, onion, olives, capers, grilled bread, and the asparagus. Toss well and set aside for 30 minutes before serving.