Preheat oven to 400 degrees F.
Get all your ingredients prepared. Dice your veggies, shred your cheese, dice your herbs, and set all aside.
Whisk the eggs and milk together with a pinch of salt and pepper. Set aside.
Add butter to cast iron skillet over medium heat. Melt butter then add diced potatoes with salt, pepper and 1/4 teaspoon of garlic powder. Cook for 3-4 minutes, moving around every 20-30 seconds or so.
Add sliced onions and cook for 3-4 more minutes, moving around with a rubber spatula every 20-30 seconds.
Add spinach, fresh herbs and the other 1/4 teaspoon of garlic powder. Stir with rubber spatula and cook for another 2-3 minutes, until spinach is a bit wilted.
Add remaining veggies (mushrooms + asparagus) and cook another 2 minutes or so. Using the rubber spatula, flatten down a little bit then add your shredded cheese and let it melt for about a minute.
Pour the eggs on top, making sure it covers up all the veggies and cheese. Let it cook for a minute or two in the pan then toss in the oven and cook for 13-15 minutes until fully cooked.
Serve warm with hot sauce or sour cream, if you'd like! If you have leftovers, they can stay in the fridge for 1-2 days or freeze for later.