Before grilling, soak the toothpicks or skewers in water for 30 minutes to prevent them from burning. Butterflying the chicken -- splitting each piece in half and fanning it open like a book -- creates two layers. They make tasty "sandwiches" with tomato and basil.
Meaty beefsteak tomatoes are easily found in most supermarkets and are the go-to choice for thick slices on burgers or BLTs. When stuffed and baked, as here, they are meltingly delicious. Don't waste a bit of these amazing tomatoes -- use the insides you scoop out here to make a simple Spanish appetizer called Pan con Tomate, below.
We used a colorful combination of beefsteak and red, yellow, and orange cherry tomatoes, but any ripe tomatoes would work. Serve the salad as a sandwich condiment or a side dish for grilled fish or chicken.