First, crack your eggs into a small bowl and beat them together well with a fork.

Heat a nonstick pan over medium heat and add the olive oil. Add the diced onion and saute for 3 to 5 minutes.

Add the chopped peppers and cook for 1 to 2 minutes or just until the bell peppers are slightly tender. Turn off the heat.

Using a slotted spoon, lift the onions and peppers (leaving behind the oil) out of the skillet and transfer to the reserved beaten eggs and combine well. Then add the spinach and mix.

Add the butter or margarine and give the pan a quick tilt to make sure the butter coats the entire bottom of the pan.

Pour in the egg mixture and sprinkle it all with a dash of salt and pepper.

Tilt the pan and lift the edges of the omelette as it starts to cook in order to allow the uncooked parts in the middle to flow out to the edges of the pan and cook quicker and more evenly. Then add the cheese, but don't let the cheese get too hard too quick, but allow it to melt.

Allow your vegetable omelette to cook until the bottom of the eggs is solid but not brown at all.

Then, using a rubber spatula, either flip it over entirely and let it cook for 1 to 2 minutes before transferring to a plate. Or, fold the omelette in half and slide it off the pan onto a plate. The interior should be creamy but not raw.