Rinse and drain spinach and basil; wrap in towels. Chill in a plastic bag.
Meanwhile, cut bread into 1-inch chunks and put in an 11- by 17-inch roasting pan. Bake in a 350° oven until chunks are light golden and soft parts of bread are crisp, about 30 minutes, stirring occasionally. Let cool.
Cut tomatoes into 1- to 2-inch chunks and place in a large bowl. Scoop juice from cutting board into bowl and add garlic, oil, vinegar, chilies, and salt and pepper to taste.
Gently mix tomatoes with bread, red peppers, and olives. Let stand at least 15 minutes, stirring occasionally, for bread to soften. Gently mix in spinach and basil. Scatter salad with capers and crisscross anchovies on top.