Preheat broiler. Put bread slices on a large baking sheet, brush both sides with olive oil (about 6 tbsp.), and sprinkle with salt and pepper to taste. Broil bread on both sides until golden and crunchy, about 2 minutes per side. When toasts are cool enough to handle, rub each on one side with garlic halves. Lower heat to 325°.
Zest 1 lemon (to yield 1 tsp. zest) and squeeze half of it (to yield 2 tsp. juice). Cut other lemon into wedges. In a large mixing bowl, whisk together 3/4 tsp. salt, 1/4 tsp. pepper, lemon zest, lemon juice, and 2 tbsp. olive oil. Add beans and toss gently to mix. Set aside.
With a very sharp knife, make shallow slashes about 1 in. apart in skin of snapper fillets. Season fillets with salt and pepper. Heat 1 tbsp. olive oil in a large nonstick frying pan over medium-high heat. Add 4 fillets skin side down, reduce heat to medium, and cook 5 to 6 minutes, pressing often with spatula to keep them as flat as possible; turn over and cook another 2 minutes. Transfer to a baking sheet and reserve pan juices in a bowl. Wipe pan clean with paper towels and cook remaining fillets the same way, reserving pan juices and transferring to baking sheet. Put fish in oven and cook until done, about 8 minutes (cut to check).
Add arugula and tomatoes to beans and toss gently but thoroughly. Divide salad among 8 plates, arranging in center.
Set toasts, garlicky side up, on salads and top toasts with snapper fillets, skin side up. Drizzle each fillet with a bit of pan juice, then top with about 1 tbsp. tapenade and a parsley sprig, and a drizzle of olive oil. Garnish each plate with a lemon wedge. Drizzle some olive oil over each.
Note: Nutritional analysis is per serving.