Preheat oven to 450°F.
In a large cast-iron skillet, heat 2 teaspoons olive oil over medium-high heat.
Add the onion and sauté until soft, about 4 to 5 minutes. Add the garlic and cook for another 30 seconds.
Add the sausage and cook until browned and crumbly, approximately 7 to 8 minutes. Turn off the heat and tilt the skillet and spoon out most of the rendered grease.
Turn the heat back to medium, and stir in the spinach, sun-dried tomatoes, vinegar, red pepper flakes, and salt. Cook for 2 minutes, stirring to fully mix.
Remove from heat and then stir in ½ cup of the smoked cheddar. Transfer filling to a bowl and then wipe out the cast-iron skillet with a paper towel.
Brush bottom of the cast iron skillet with 2 teaspoons of olive oil and sprinkle with cornmeal.
On a lightly floured counter, roll the dough into a 12 to 13-inch circle (if using a 10-inch skillet. (Roll out to 13 - 15 inches if using a 12-inch skillet).
Fold the dough in half, and then fold over again to create a quarter circle. Transfer to the skillet and gently unfold, pressing the dough to the bottom and sides of the skillet.
Add sausage mixture over the dough and then sprinkle over the top the remaining 1 cup of cheddar and the mozzarella.
Bake until golden brown, approximately 17 minutes. Tent with foil after about 12 minutes if browning too much on top.
Let stand for 10 minutes before slicing and serving.