Whisk eggs, milk, salt, and pepper together until a little foamy. Set aside while prepping the remaining ingredients.
In a skillet over medium heat, melt 1 tablespoon butter. Add onion and garlic and cook until softened. Add mushrooms and cook until mushrooms release excess moisture, 2-3 minutes. Add the spinach and stir while cooking until spinach is just wilted. Remove from pan and set aside on a plate until ready to fill the omelet.
Add a tablespoon of butter to the skillet over medium heat and swirl so that melted butter covers the pan. Pour the egg mixture into the pan and lightly scramble it with the back of a fork or rubber spatula for 30-40 seconds.
When eggs begin to set, stop stirring. Spread the omelet into an even layer and allow cooking for another 30 seconds. Gently test the edges of the eggs with a spatula for release from the pan.
Once the eggs are barely translucent and nearly set, but not firm, slide the pan off heat. Add the cheese and spinach-mushroom mixture to one side. Gently slide a spatula under the opposite side and fold over the filling. Cover with a lid and allow to set for 1-2 minutes to melt the cheese.
Transfer to a plate and garnish with slices of avocado, fresh tomatoes, basil, and feta.
Notes
Nutritional info includes omelet and garnishes.RECIPE TIPS:
SPECIAL EQUIPMENT: Use a well-seasoned 10-12 inch cast-iron skillet or other non-stick skillet
Eggs cook quickly, it is important to have all ingredients prepped before beginning cooking the eggs.
Add salt to the eggs 15 minutes before cooking.
Use only full-fat cream, milk, sour cream, etc., to avoid watering down the eggs.
All fresh ingredients like meat or vegetables should be cooked prior to adding.
Optional Add-Ins:
Fresh herbs and aromatics like thyme, basil, cilantro, parsley, chives, savory, green onion, leek, garlic
Fresh greens like spinach, rainbow chard, Tuscan kale, or arugula (should be wilted before adding)
Fresh tomatoes and vegetables like zucchini, bell pepper, green chiles, asparagus, mushrooms (should be cooked before adding)
Sun-dried tomatoes, canned artichokes, deli olives (drained)
Cheeses like goat cheese, cheddar, feta, pepper jack, gouda, gruyere, brie, and parmesan.
Smoked ham, prosciutto, speck are fully cooked and can be added without pre-cooking