In ancient Native American kitchens, a built-in outdoor pizza oven called a 'horno' was used. These ovens were made of adobe or clay and were used to bake a variety of bread, including flatbreads resembling pizzas. Native Americans enjoyed toppings such as corn, beans, and wild game on their flatbreads, creating a nutritious and flavorful dish. The 'horno' was a vital part of the Native American kitchen, allowing them to cook their pizzas in an outdoor setting, utilizing the natural heat and smoky flavors of the oven.