If using leftover noodles, bring them to room temperature. If cooking fresh, boil noodles according to package directions, drain, and toss with a little oil to prevent sticking. Set aside.
In a large bowl, whisk together eggs, milk or cream (if using), salt, and pepper. Stir in vegetables, cheese, and protein of your choice. Add herbs or spices if desired.
Heat 2–3 tablespoons of oil or butter in a large non-stick skillet over medium heat. Spread the noodles evenly across the pan and press down lightly to form a flat layer. Cook for 4–5 minutes until the bottom is golden and crispy.
Pour the egg mixture evenly over the noodles. Reduce heat to low, cover, and cook for 8–10 minutes until the edges are set and the center is almost firm.
If the top is still runny, either place the skillet under a broiler for 1–2 minutes (if oven-safe) or carefully flip the frittata by sliding it onto a plate, inverting it back into the skillet, and cooking 2–3 more minutes.
Slide the finished frittata onto a board, slice into wedges, and garnish with herbs, green onions, or a drizzle of soy sauce or hot sauce. Serve warm.