Tuscan Tuna Salad

1 (15 ounce) can cannellini beans
1 can (5 to 6-ounce) tuna packed in water, drained and flaked with a fork
2 tablespoons finely chopped flat-leaf parsley
2 tablespoons finely chopped red onion
1 tablespoon extra-virgin olive oil
1 tablespoon lemon juice
1/4 teaspoon sea salt
Freshly ground pepper, to taste
1 small sourdough boule, cut into 1/2-inch-thick slices, drizzled with olive oil and toasted or grilled
1/3 cup chopped walnuts, toasted (optional)

Drain and rinse beans and combine with flaked tuna in a bowl. Stir in parsley, red onion, olive oil, lemon juice, walnuts if using, salt and pepper. Taste and adjust seasoning. Pile on toasted sourdough and serve immediately.