We're loving this turkey grilled cheese recipe for our leftover thanksgiving turkey. Take the all-American grilled cheese sandwich to a whole new level with the addition of caramelized sweet onion. This is a powerful way to add great flavor to burgers, homemade pizzas, soups, grilled meats, and just about anything. Here’s a quick tutorial on caramelizing onions: Heat a dab of olive oil in a skillet and add diced or sliced sweet onions. Cook, stirring occasionally, until onions begin to turn golden and liquid has evaporated. Continue to cook until onions develop a deep golden-brown color.