Seasoning mix: Add chili powder, cumin, garlic powder, onion powder, paprika, oregano, black pepper, cayenne pepper and salt to bowl, mix well.
Marinate chicken in ziplock bag with 1 tbsp olive oil and 1 1/2 tsp of seasoning mix, at least 30 min up to 24 hrs.
Preheat oven to 350. In Dutch oven heat 1 tbsp olive oil over medium heat and cook diced onion 5-7 mins stirring often. Add 1 cup water and dissolve 1/2 a chicken bullion cube (or add 1 cup chicken broth). Add tomato sauce, minced chipotle, and remainder of seasoning mix, and mix well. Add chicken breast and cover breast with sauce. Bring to simmer, cover and place in oven. Bake 40-45 mins. Remove from oven and shred chicken with forks and mix in sauce well. Let stand 5-10 mins for sauce to thicken. If doesn't thicken to your liken, place on stove top over low heat until sauce reduced.
While chicken standing increase oven heat to 375. Taco shells: heat corn tortilla in microwave about 30 seconds. Spritz each side of tortilla with olive oil and heat in oven for 10 mins hanging directly from oven rack to form taco shells. This step can be skipped but is my preferred method. Use pre made crispy tacos or just soft corn or flour tortillas to save time. Cooking the corn tortillas this way creates a pliable taco shell and holds together well while eating, I hate a taco falling apart half way through eating it. I would credit whoever came up with this taco shell method if I knew, so props to whoever you are.
Add chicken and your favorite taco toppers to complete. I enjoy these with a little shredded romaine or iceberg, shredded Colby jack and sour cream. Again these have bold flavor, and decent spice with the cayenne and chipotle so hot sauce/salsa is optional.