Combine spinach, herbs, radishes, and onions.
Combine eggs and water, and add to greens mixture.
Heat a cast iron skillet or omelet pan to medium-high heat.
Add just enough oil to pan to coat the bottom.
Pour in omelet mixture, pushing cooked edges of omelet toward center of the pan with a metal spatula, and tipping the pan so the liquid will run to the outside rim and cook.
When the omelet is almost set and the bottom is a golden brown color, lift up one side and fold it over the other side.