Pesto Egg Salad Sandwiches

Ingredients

• 1/2 cup fat-free mayonnaise
• 1/4 cup finely chopped red onion
• 4 teaspoons prepared pesto
• 1/4 teaspoon salt
• 1/8 teaspoon pepper
• 4 hard-boiled large eggs, chopped
• 3 hard-boiled large egg whites, chopped
• 8 slices whole wheat bread, toasted
• 8 spinach leaves