Cheesy Chicken Burger

INGREDIENTS:

• 8  good-quality or fresh burger buns, split
• 8 sprigs of fresh flat-leaf parsley
• 1 pound ground dark-meat chicken
• 1 large free-range egg
• Salt and freshly ground pepper
• freshly ground black pepper
• 2 tablespoons vegetable oil, such as safflower
• 1/2 cup mayonnaise
• 3 tomatoes thinly sliced
• 2 medium red onions, thinly sliced
• 2 tablespoons fresh lemon juice
• 1 celery stalk, finely chopped
• 6 slices Cheddar cheese 

METHOD:

1. In a large skillet, heat 1 tablespoon vegetable oil over medium. Add onion, black pepper, lemon juice, celery stalk, with salt and ground pepper. Cook, stirring occasionally, until tender, 8 to 10 minutes. Transfer to a medium bowl; cool to room temperature. 
2. Add chicken to vegetable mixture in bowl with 1/2 teaspoon salt and 1/4 teaspoon ground pepper. Mix to combine. Shape mixture into four 4-inch-wide patties.
3. In reserved skillet, heat remaining tablespoon oil over medium; cook patties until browned and cooked through, 6 to 8 minutes per side. Place chicken on burgers buns, and top with lettuce, tomato, mayonnaise, boiled egg slices and Cheddar Cheese slices.
4. Close the burgers and serve right away.