Preheat the Oven: Preheat the oven to 180°C / 350°F.
Heat the Oil: Warm the extra virgin olive oil in a large oven-proof skillet over medium heat.
Cook the Onion: Add the diced yellow onion to the skillet and cook, stirring frequently, until the onion becomes translucent.
Wilt the Kale: Add the de-stemmed, thinly sliced lacinato kale and cook, stirring frequently, until the kale has wilted.
Season the Vegetables: Season the cooked onion and kale with a little salt and pepper.
Add the Pumpkin: Scatter the cubed roasted pumpkin evenly over the cooked kale and onion mixture.
Add the Goat Cheese: Sprinkle the crumbled goat cheese over the pumpkin and vegetables.
Whisk the Eggs: Crack the eggs into a large bowl and whisk them together with the milk, if using.
Add the Egg Mixture: Pour the egg mixture evenly over the kale, pumpkin, and goat cheese, then gently shake the skillet to help distribute the eggs throughout the vegetables.
Transfer to the Oven: Remove the skillet from the stovetop and place it in the preheated oven.
Bake the Frittata: Bake for 5–10 minutes, until the frittata begins to set.
Broil the Top: Switch the oven to the broil setting and broil for about 5 minutes, watching closely so the top becomes puffed and golden without burning.
Check for Doneness: The frittata is ready when the top is puffed and golden and the center jiggles only slightly when the pan is gently shaken.
Cool Before Slicing: Remove the skillet from the oven and let the frittata cool for a few minutes before slicing and serving.