Preheat your oven to 325 f. and lightly spray a standard 12-cup muffin tin generously with avocado oil cooking oil spray.
In a large bowl, whisk the eggs, milk, cheese, sea salt, and pepper. Set aside.
Heat the oil in a large skillet and sauté your mushrooms until they start to brown.
Stir in the onion, bell pepper, garlic, and oregano. Continue to saute for 2-3 minutes.
Add in the spinach and cook, stirring constantly, until just wilted, about 1-2 minutes. Remove the skillet from heat.
Stir your sauteed veggies into the egg mixture, then divide this mixture equally among your prepared muffin cups.
Bake for 20-25 minutes or just until the eggs are set and puffed.
Allow to cool slightly before carefully removing them from the tin.
Enjoy!