Cheesy Avocado Chicken Melt Sandwich - chefmelt

Ingredients

• 4 bread slices.
• 4 cheese slices.
• 1 small red onion.
• 1 tablespoon Dijon mustard.
• 2 chicken breasts.
• Salt and pepper.
• Butter for grilling.
• 1 avocado, sliced.
• 2 tablespoons mayo.
• 1 tomato.
• 1 tablespoon olive oil.