Puffy Chicken Tacos

Name: Puffy Chicken Tacos
Ingredients: ¼ cup olive oil; 2½ lb. bone-in, skin-on chicken thighs; Kosher salt and freshly ground black pepper, to taste; 6 cloves garlic, finely chopped; 1 medium yellow onion, finely chopped; 1 rib celery, finely chopped; 1 small carrot, finely chopped; 1 small red bell pepper, finely chopped; 3 cups chicken stock; 1 14-oz. can whole peeled tomatoes in juice, crushed by hand; 2 avocados, pitted, peeled, and mashed; 2 cloves garlic, minced; Juice of 1 lime; Canola oil, for frying; 3 cups masa harina (available from Amazon.com); 1½ tbsp. unsalted butter, softened; Shredded iceberg lettuce, diced tomato, and shredded cheddar cheese, to garnish