Creating your healthy breakfast sandwich is straightforward if you follow these easy steps:

1. Preheat your skillet: Place a non-stick skillet over medium heat and add olive oil or cooking spray.

2. Cook the egg: Crack the egg into the skillet. Season with salt and pepper. Cook until the egg is set to your liking, about 3-5 minutes.

3. Prepare the bread: While the egg is cooking, toast the slices of whole grain bread until golden brown.

4. Assemble the sandwich: Once the egg is ready, layer the spinach leaves on one slice of toasted bread.

5. Add the egg: Place the cooked egg atop the spinach.

6. Add cheese (if using): Lay a slice of low-fat cheese on top of the egg, allowing it to melt slightly.

7. Layer avocado and tomato: Add the slice of avocado and the slice of tomato on top of the cheese.

8. Finish with the second slice of bread: Top with the second slice of toasted bread to complete the sandwich.

9. Slice and serve: Carefully cut the sandwich in half and serve while warm for the best taste.

Following these steps, you will create a delightful healthy breakfast sandwich that not only satisfies your hunger but also nourishes your body.