Italian-Style Tuna Salad

3 tablespoons olive oil

1 tablespoon red wine vinegar

salt and ground black pepper to taste

2 slices Italian bread

cubed

3 tomatoes

cut into small pieces

1 medium cucumber

peeled and thinly sliced

1 small onion

thinly sliced

1 (5 ounce) can tuna

drained

20 black olives

1 tablespoon capers