Preheat the oven to 400°F
Add 1 teaspoon vegetable oil to a 10 inch, oven safe skillet over medium heat. Add the diced potato and season with salt and pepper.
Cook, stirring occasionally, for about 5 minutes, until the potatoes are almost cooked through.
Add the green onion and broccoli and stir to combine. Cook for 5 more minutes.
Meanwhile, add the 6 eggs to a bowl and beat gently with a fork. Add the 3 tablespoons of milk and ½ cup of cheddar cheese and stir to combine the ingredients evenly.
Turn the heat down to medium-low. Add the egg/milk/cheese mixture to the vegetables, briefly stir to evenly distribute the ingredients. Let the pan sit for 5 minutes over the medium-low heat while the bottom of the frittata sets.
Move the pan to the preheated oven. Cook for 10 minutes.
Remove the pan from the oven (using a hot mitt!). If the center is set, your frittata is done. If not, return it to the oven for several more minutes.
Allow the frittata to cool for a few minutes before cutting and serving.