Preheat oven to 375°F.
In a medium bowl, whisk together eggs, ricotta cheese, Parmesan cheese, thyme, salt and pepper until well mixed. Set aside.
In a 10-inch cast iron or ovenproof skillet, add olive oil and cook sliced onion over medium heat for about 5 minutes until translucent.
Add spinach and cooked bacon or chorizo (optional) to the skillet and pour the egg mixture over the spinach.
Transfer the skillet to the oven and bake for 15-20 minutes or until the center is just set.
Allow the frittata to cool. Turn frittata out onto a serving platter and slice into wedges or serve in the skillet.
To serve, spoon Rao’s Homemade Arrabbiata sauce on top and add avocado slices. Serves 4-6.