DRESSING:
If you like, spread the bread chunks out on a baking sheet, ton-based salad can eas- drizzle with oil, and toast in a 400°F oven until golden.
Blanch the green beans in a pot of boiling water for a minute or two, then plunge into a bowl of cold water to stop them from cooking.
Drain well and pat dry with paper towels, so that they don't sog out the croutons.
Put the toasted croutons (or fresh bread chunks) into a wide bowl with the green beans, white beans, mozzarella, tomatoes, onion, olives, basil, and capers (if using). Grind fresh pepper overtop.
In a jar or small bowl, shake or stir together the oil, vinegar, lemon juice, and mustard; drizzle over the salad and toss with tongs to coat. Serve immediately.