Egg Salad Sandwich

INGREDIENTS

• 4 hard-cooked egg whites, chopped
• 1/2 avocado, pitted and diced medium
• 1/4 small red onion, diced small
• 1 teaspoon mayonnaise
• 1 teaspoon sour cream
• 1 teaspoon Dijon mustard
• Coarse salt and ground pepper
• Whole grain bread, for serving
• Arugula, for serving