3 tablespoons olive oil
1 pound boneless, skinless chicken breasts (cut crosswise into 1-inch-wide strips)
  Salt and freshly ground black pepper
1 large yellow onion (cut in half lengthwise and thinly sliced crosswise, about 3 cups)
3 cloves garlic (large cloves, finely minced)
1 pinch red pepper flakes (or to taste)
12 ounces Lacinato kale (also called dino or Tuscan kale, stems discarded and leaves sliced crosswise into 1/2-inch-wide ribbons, about 8 cups)
1/3 cup white wine
8 ounces Pear or cherry tomatoes (about 1-1/2 cups)