In a large skillet over medium heat, heat 1 tablespoon of oil. Add the garlic and sauté for 1-2 minutes, until fragrant. Remove garlic and place aside. Add the other tablespoon of oil and the other vegetables to the skillet and let cook for 5 minutes. Add the baby spinach and allow it to wilt. Remove from heat and add to the garlic.
Spray a 13x9" baking dish with nonstick spray. Spread the shredded potatoes along the bottom of the dish, pressing to spread evenly. Add the vegetable mixture.
Whisk together the eggs and egg whites, milk, and pepper. Pour over the prepared veggies. Sprinkle the cheese over the top and the rest of the pepper.
Bake, uncovered, until the cheese melts and the top begins to golden, about 45-50 minutes. Slice and serve. Top with sliced avocado and salsa or hot sauce, to taste.