Heat a medium nonstick skillet over medium heat and spray with olive oil cooking spray. To test if your pan is ready, flick a few drops of water onto the surface; they should sizzle gently.

Add the chopped mushrooms and cook, stirring occasionally, until they release their water and start to brown, about 4 to 5 minutes.

Add the fresh spinach to the skillet and cook until wilted, about 1 minute. Season lightly with a pinch of salt.

While the spinach is wilting, whisk the eggs in a small bowl until well combined and slightly frothy.

Pour the eggs into the skillet over the mushrooms and spinach, then let sit undisturbed for 30 seconds.

Cook, gently folding with a spatula every 20 to 30 seconds, until the eggs are almost set but still slightly glossy, about 2 to 3 minutes.

Stir in the shredded cheddar cheese, salt, and pepper. Continue to cook until the cheese is melted, about 30 to 60 seconds.

Remove from heat while eggs are still slightly creamy.

Garnish with fresh chives or parsley if desired, and serve immediately.