1 (14- to 15-oz) can cannellini beans, rinsed and drained
2 garlic cloves, finely chopped
1 tablespoon fresh lemon juice
2 tablespoons olive oil
2 tablespoons chopped fresh flat-leaf parsley or basil
1/4 teaspoon salt
1/4 teaspoon black pepper
2 (6-oz) cans Italian tuna in oil, drained
2 tablespoons finely chopped fresh basil or flat-leaf parsley
1/4 cup pitted Kalamata or other brine-cured black olives, finely chopped
1 celery rib, finely chopped
2 tablespoons finely chopped red onion
2 tablespoons olive oil
1 tablespoon fresh lemon juice
1/4 teaspoon salt
1/8 teaspoon black pepper
8 (1/3-inch-thick) slices rustic Italian bread (from a round crusty loaf) or 4 (4-inch-long) oval panini rolls
1 cup loosely packed trimmed watercress sprigs