Preheat oven to 350 degrees.
Heat pan over medium high and add half of the olive oil, ground chicken, and black pepper. Cook until done then set aside on a plate, about 3- 5 minutes.
Using the same pan, add the rest of the olive oil, onion and shiitake mushrooms and stir over medium heat until onions are translucent. Set aside.
Whisk eggs in a mixing bowl and add milk then stir.
Spray nonstick cooking oil to muffin baking pan.
Disperse chicken, onion and shiitake mushrooms evenly into each muffin mold.
Gently pour whisked egg to fully cover ingredients in each mold (but not all the way to top). Top with shredded cheese.
Bake in oven for 20 minutes. Check middle of muffin with toothpick to check to see it’s fully cooked. Enjoy!