Preheat the oven to 400 degrees F with a baking stone. In a electric mixing bowl, whisk the yeast, water and oil together. Add the flour and salt and mix, using a dough hook, until the dough comes away from the sides and crawls up the dough hook. Remove the dough from the bowl. Grease the bowl with olive oil and place the dough back in the bowl. Cover the bowl with plastic wrap and let the dough rise until double in size, about an hour. Turn the dough out onto a floured surface and divide dough into 4 (4-ounce) portions. Roll the dough into balls, cover and let the dough rest for 15 to 20 minutes. Press the dough out into 4 individual pizzas, about 6 inches in diameter and 1/4-inch thick. Spread 1/4 cup of the tomato sauce evenly over each pizza dough. Sprinkle each pizza with 1-ounce of the ham and 1-ounce of the cheese. Bake the pizzas in batches. Using a pizza peel carefully place two of the pizzas on the baking stone. Bake the pizzas for 15 to 20 minutes or until golden brown. Remove the pizza from the oven and slice into 4