Heat a stove-top grill. Brush the bread with olive oil, sprinkle with salt, and grill for 10 minutes on each side, until nicely browned. If you don't have a stove-top grill, heat the oil in a large sauté pan, add the bread and salt; cook over low to medium heat, tossing frequently, for 10 minutes, or until nicely browned. Add more oil as needed.
For the vinaigrette, whisk together the garlic, mustard, vinegar, olive oil, salt, and pepper.
In a large bowl, mix the tomatoes, cucumber, red pepper, yellow pepper, red onion, basil, and capers. Toss with enough vinaigrette to moisten. Season liberally with salt and pepper and arrange the vegetables artfully on a platter. Drizzle the bread with extra vinaigrette or olive oil and add to the platter.
Serve immediately, or allow the salad to sit for about half an hour for the flavors to blend.