Heat olive oil in a non-stick pan over medium heat. Add onions, peppers, and mushrooms, cooking until tender (3-5 minutes). Toss in spinach and cook until wilted (about 1 minute). Transfer veggies to a bowl and wipe the pan clean1.

Whisk eggs with water and a pinch of salt until frothy.

Return the pan to medium heat and melt butter until bubbly. Pour in egg mixture.

As eggs begin setting, use a spatula to gently push cooked portions toward the center, tilting the pan to let uncooked egg flow to empty spaces.

When eggs are nearly set, add your cooked veggies to one half of the omelet and sprinkle cheese on top.

Fold the empty half over the filling and slide onto a plate.