How to Make It
Broil bell pepper halves on an aluminum foil-lined baking sheet 6 inches from heat, until peppers look blistered, 8 to 10 minutes. Transfer to a bowl, and cover with plastic wrap; let stand until softened, about 10 minutes. Remove and discard plastic wrap. Remove and discard skin, stem, and seeds from bell pepper. Thinly slice flesh; set aside.
Bring a large saucepan of water to a boil. Add haricot verts, and cook until bright green and al dente, about 2 to 3 minutes. Drain and place in an ice bath; let stand 10 minutes until chilled. Drain; cut diagonally into 1 1/2-inch pieces.
Stir together capers, parsley, chives, vinegar, tarragon, mustard, salt, black pepper, and garlic in a medium bowl. Slowly drizzle in oil in a steady stream, whisking constantly, until thoroughly combined. Brush 2 tablespoons of the dressing on cut side of top half of ciabatta.
Place 1 cup of the beans in a medium bowl; coarsely mash. Stir in 2 teaspoons of the dressing and remaining 1 cup beans until combined. Spread bean mixture on bottom half of ciabatta.
Toss together roasted red pepper slices, haricot verts, fennel, onion, olives, and remaining 2 tablespoons dressing in a medium bowl. Top bean mixture with vegetable mixture and top half of ciabatta. Wrap sandwich tightly in plastic wrap, and then again in aluminum foil. Place on a baking sheet, and place another baking sheet on top. Place a heavy skillet on top baking sheet, and press gently to flatten. Chill at least 1 hour, up to overnight before serving.