1. Preheat the oven to 375 degrees F (190 degrees C).

2. Peel and slice the potatoes and carrots into thin rounds.

3. Heat some olive oil in an oven-safe skillet over medium heat. Add the potatoes and carrots and cook until softened, about 10 minutes.

4. Meanwhile, whisk together the eggs, oregano, salt, and pepper in a large bowl.

5. When the potatoes and carrots are soft, add the diced tomatoes to the skillet. Cook for another 5 minutes or so, until the tomatoes have released some of their juices.

6. Pour the egg mixture into the skillet and stir everything together. Let cook for a few minutes until the edges start to set.

7. Sprinkle the grated Pecorino Romano over the top of the frittata.

8. Transfer the skillet to the preheated oven and bake for 15-20 minutes, until the frittata is cooked through and golden brown on top.

9. Let cool for a few minutes before slicing and serving.