Heat oil in skillet over medium heat and sauté onions about 5 minutes until soft.
Stir in garlic, followed by oregano, cumin, paprika, chopped chipotle, and toast for 1 minute.
Add in the fire-roasted tomatoes, stock, and salt. Bring to a simmer, and cook for 4-5 minutes.
Let cool and and then transfer to a blender and purée until smooth.
Pour the sauce back into the skillet, add the hredded chicken and cook until heated through. Taste and adjusting seasoning, if needed.
Serve in tortillas with topping of your choice.