Preheat oven to 300 degrees F. Place tomatoes in an even layer in a large shallow glass baking dish. Drizzle with olive oil, and sprinkle with basil, salt, and pepper. Bake, uncovered, for 1 1/2 to 2 hours or until tomatoes are slightly dried and charred. Cool slightly (15 minutes).
On a large serving platter spoon tomatoes and the pan juices over spinach.