1. 1. Peel and chop the hard-boiled eggs into small pieces.

2. 2. Finely chop the red onion.

3. 3. In a mixing bowl, combine the chopped eggs, red onion, mayonnaise, and mustard.

4. 4. Mix well until all ingredients are evenly incorporated.

5. 5. Season with salt and pepper to taste.

6. 6. Refrigerate for at least 30 minutes before serving.