Heat oil in a large skillet over medium heat. Add onion and garlic; sauté 4 minutes. Add oregano, cumin, and chipotle chile; cook 1 minute. 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 (to avoid splatters); 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.