Heat olive oil or butter in a non-stick skillet over medium heat, then sauté diced bell pepper for 2-3 minutes until slightly softened.

Add spinach to the skillet and cook until it wilts, signaling it's ready in about 1 minute.

In a small bowl, whisk together the eggs with milk (if using), salt, and pepper.

Pour the egg mixture into the skillet with the cooked vegetables and let it sit undisturbed for about 30 seconds until the edges begin to set.

Gently push the cooked egg from the edges towards the center of the pan, tilting the pan to allow any uncooked egg to flow underneath; continue this process, gently folding, until the eggs are mostly set but still retain a slight moistness.

If desired, stir in shredded cheese, then immediately remove from heat to prevent overcooking, and serve warm.