Heat oil in a large skillet over medium heat. Add onion and garlic, sauté 4 minutes.
Add oregano, cumin, and chipotle chile, cook 1 minutes.
Add tomato stock, and adobo; bring to a simmer. Cook 7 minutes.
Place tomato mixture in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Cover opening with a kitchen towel and blend until smooth.
Return sauce to pan over low heat. Add chicken and salt; cook 1 minute.
Divide mixture among tortillas. Top evenly with sour cream, cilantro, avocado, and cheese. Serve with lime.