Chicken Salad Melt - Warm Sandwich Treat - Tasty Hush

Ingredients

• 1/4 cup mayonnaise.
• 1/4 cup Greek yogurt.
• 1/4 cup celery, minced.
• 1/4 cup red onion, sliced thin.
• 1 cup rotisserie chicken, shredded.
• 2 teaspoons lemon zest.
• 2 teaspoons Dijon mustard.
• 1/4 teaspoon salt.
• 1/4 teaspoon ground pepper.
• 8 slices whole-grain bread.
• 1 medium tomato, cut into slices.
• 4 slices American cheese.
• 2 tablespoons melted butter, unsalted.