1. 1. Preheat the oven to 350°F (180°C).

2. 2. Peel and dice the potatoes into small cubes.

3. 3. Heat some oil in a skillet over medium heat.

4. 4. Add the diced potatoes and cook until they are golden brown and cooked through.

5. 5. Slice the red onion, green onions, and fresh tomatoes.

6. 6. Add the sliced onions and tomatoes to the skillet with the potatoes and cook until softened.

7. 7. In a bowl, whisk the eggs and season with salt and pepper.

8. 8. Pour the egg mixture over the vegetables in the skillet.

9. 9. Sprinkle shredded cheddar cheese on top of the frittata.

10. 10. Transfer the skillet to the preheated oven and bake for about 15-20 minutes, or until the eggs are set and the cheese is melted and bubbly.

11. 11. Remove from the oven and let it cool slightly before slicing and serving.