1. Heat oven to 450 degrees. Place potatoes on a baking sheet lined with parchment paper; roast until browned, about 30 minutes. Meanwhile, roast red pepper over gas burner until charred on all sides. Place in a bowl; cover with plastic wrap. Set aside for 15 minutes. Remove skin and seeds; cut into 1-inch pieces.

2. Fill a bowl with water and ice; set aside. Bring a pot of water to a boil; add haricots verts. Cook until bright green and just tender, about 2 minutes. Drain; transfer to the ice bath until cool. Drain again, and set aside.

3. Place basil, vinegar, salt, pepper, and 2 tablespoons warm water in a blender, and puree until smooth. With motor running, add olive oil, and puree until combined. Set aside.

4. In a large bowl, combine spinach, tomatoes, celery, cucumbers, scallions, roasted potatoes and peppers, reserved basil puree, and tuna; toss. Divide haricots verts among six plates; top with tuna salad. Garnish with chopped Kalamata olives, and serve.