1/2 cup finely chopped red onion, soaked in ice water for 20 minutes, then drained and patted dry
3/4 cup pitted and chopped herb-marinated olives
3 tablespoons lemon juice
1 tablespoon chopped fresh oregano
2 cups baby arugula
Salt and ground black pepper
Heat the grill to medium.
Lightly mist the bread on both sides with the olive oil cooking spray. Grill the bread on the grill until nicely toasted, about 2 minutes per side. Once the bread is grilled, rub one side of each slice with the cut side of the half clove of garlic. Set aside.
In a large bowl, use a potato masher or fork to mash 1/2 cup of the beans. Add the remaining whole beans, the olive oil, tuna, celery, red onion, olives, lemon juice, oregano, minced garlic and arugula. Mix gently, then season with salt and pepper. Divide the bean mixture between the slices of bread, mounding it on each. Serve with a fork and knife.