Preheat the broiler. In a large bowl, mash the whole garlic clove with the 1/2 teaspoon of coarse salt until a paste forms. Add the lemon zest and lemon juice and mix until combined. Add the artichoke hearts, tuna, onion, celery, tomatoes and basil to the bowl and dress with 3 tablespoons of the EVOO. Mash the tuna salad with a fork and season to taste with salt and pepper.
Preheat the broiler. Place the bread slices on a broiler pan and char on both sides under the broiler. Rub 1 side of each slice with the cut garlic and drizzle with the remaining 1 tablespoon of EVOO. divide the arugula and the tuna salad among the bread slices and top with the cheese. Return to the broiler and melt the cheese until bubbly, 1 to 2 minutes.