FILLING: In a large skillet over medium heat, add olive oil and onion; sauté for 4 minutes or until tender, stirring occasionally. Add garlic and cook for 30 seconds more. Stir in chipotle peppers, oregano, and cumin, toast for 1 minute. Add the crushed tomatoes, stock, and salt. Bring to a simmer, cook for 7 minutes.
Carefully pour the tomato mixture into a food processer or blender, and blend until smooth.
Return the blended sauce to the pan over low heat. Add the cooked chicken, cook for 5 minutes. Taste adding more salt if needed.
TORTILLAS: Warm tortillas according to package directions or place directly over a gas flame to char the edges.
AVOCADO MASH: In a small bowl, mash the avocado, squeezed in some lime juice, sprinkle in some salt and garlic powder, spread on tortillas before adding the chicken.
TO ASSEMBLE: Top the warmed tortillas with avocado mash and chicken. Garnish with red onions, Cotija cheese and cilantro. Serve with a lime wedge.
Cook’s Note: Use one chipotle pepper for mild or two for medium heat. If you want it hot, hot, hot, go for three!