In a medium nonstick skillet over medium-high heat, heat 1 tablespoon of the avocado oil.

Add the cremini mushrooms and sauté until golden brown, about 6 minutes.

Add the garlic and shallot and cook until translucent, 2 minutes.

Add the baby spinach and cook until the spinach wilts and the water cooks out, 5 minutes.

Season with salt and pepper.

Transfer to a paper towel–lined plate and set aside.

In a medium bowl, whisk together the eggs whites, egg, and milk until light and frothy.

Add the parsley, chives, and dill.

Season with salt.

In the same skillet, heat the remaining 1 tablespoon avocado oil over medium heat.

Add the egg mixture and swirl it around the pan.

Gently stir the egg mixture with a rubber spatula, then swirl the pan, spreading the eggs around the sides of the pan.

Reduce the heat to low and cook until the egg is mostly set.

Add the mushroom-spinach mixture to the middle of the eggs.

Fold the omelet in thirds by tilting the pan and helping the top of the omelet roll over the center and onto a serving plate.

Garnish with chopped chives.

Serve immediately.