In a large dutch oven set over medium-low heat add 2 tablespoons of oil and heat until hot and shimmery. Add the diced onion and smashed garlic cloves and cook for 5 minutes, stirring occasionally, until the onion is translucent and softened (but not caramelized). Use a slotted spoon to transfer the onion and garlic to the blender, then pour the beer into the dutch oven and let it come to a simmer.
While the beer comes to a simmer, add the crushed tomatoes, chipotles, oregano and salt to the blender. Blend for 20-30 seconds until smooth. Once the beer reaches a simmer, let it cook for 5 minutes to cook off the alcohol, then stir in the tomato/chipotle mixture from the blender.
Add the chicken thighs to the sauce, making sure they are all submerged, then place the lid on and let cook over medium-low heat for 1 hour. After the thighs have cooked for an hour, turn off the heat then use a slotted spoon to remove the chicken thighs and place them in a bowl. Use two forks to shred the chicken, stir the chicken back into the sauce. Taste for salt and adjust.
To assemble your tacos, add a few tablespoons of the shredded chicken to a warm street taco size tortilla. Top your tacos with diced onion and chopped cilantro and serve with rice and beans.