Preheat oven to 375°F and spray two 9x13 baking dishes with nonstick cooking spray. Set aside.
To a large skillet, add butter and olive oil and heat over MED HIGH heat. Add ground chicken and cook, breaking apart with a wooden spoon as it cooks, for 5-7 minutes, until fully cooked. Drain in a colander and return to skillet.
Add diced onion and minced garlic and cook an additional 5 minutes until onions are tender. Add taco seasoning and cook another 30 seconds or so, stirring to combine everything well.
Remove skillet from heat then add canned tomatoes, green chilis and black beans.
Place 10 taco shells in each prepared baking dish. Spread approximately 2 Tbsp refried beans on the inside of each taco shell. Top refried beans with approximately ½ cup of the prepared taco meat mixture, then add about ¼ cup shredded cheese on top of each taco.
Place casserole dishes side by side on the same rack. Bake for approximately 10 minutes until cheese is melted, tacos are heated through and shells are crisp and starting to get golden brown.
Top with desired toppings and enjoy!