In a small bowl, whisk eggs with almond milk or water, salt, and pepper until well combined.
Heat olive oil or spray a non-stick skillet over medium-low heat.
Pour the egg mixture into the hot skillet. As the edges set, gently push the cooked egg toward the center, tilting the pan to allow uncooked egg to flow underneath.
When the omelet is mostly set but still slightly moist on top, sprinkle spinach and feta cheese over one half.
Fold the other half of the omelet over the filling. Cook for another minute until the cheese is slightly melted and the spinach is wilted.
Slide onto a plate and serve immediately with a slice of whole-grain toast.
