Add the oil to a 10” cast-iron skillet over medium heat and cook the pancetta, onions, and potatoes until tender and cooked, which takes about 10 minutes. Be sure to stir and season.
While the pancetta, onions, and potatoes are cooking, add the eggs, cheese, salt, and pepper to a medium-size bowl and whisk until completely combined and smooth.
Once the eggs are slightly runny on top, about 4 to 6 minutes, invert the frittata using a plate and place it back into the skillet runny side down, and finish cooking for 2 to 3 minutes.
Serve the frittata in the skillet or on a serving platter or plate, and garnish with additional parmesan cheese, parsley, and rosemary. Serve alongside fresh bread.