Lightly coat the bottom of a slow cooker with non-stick cooking spray. Arrange 1 pound boneless skinless chicken thighs in the slow cooker in an even layer.*
Place a medium skillet over medium heat and add 2 tablespoons unsalted butter. Once melted, add 1 medium yellow onion and cook until translucent, about 5 minutes. Add 2 chipotle peppers in adobo**, 3 cloves garlic, 1 teaspoon smoked paprika, 1 teaspoon salt, 1/2 teaspoon chili powder, and 1/2 teaspoon ground cumin, and cook for another 1 minute.
Add 14.5 ounces canned fire-roasted tomatoes, 3 tablespoons lime juice, and 1/4 cup cilantro, and simmer for 10 minutes.
Carefully transfer the sauce into a food processor (or blender). Cover and blend until smooth.
Pour the sauce over the chicken thighs. Cover and cook on LOW for 2-3 hours or until the chicken reaches an internal temperature of 165 degrees F.
Use two forks to shred the chicken. Keep warm in the crock pot or trasnfer to a serving bowl.
Place a large skillet over medium-high heat. Working in batches, cook 10 corn tortillas in the dry skillet for 1-2 minutes per side until toasted.
Assemble the tacos by adding some chicken***, red onion, cotija cheese, and cilantro to each tortilla. Serve immediately.
Notes
*If the chicken doesn't sit flat in the bottom of your slow cooker, rotate them halfway through the cook time to ensure even cooking.**For less heat, reduce the chipotle peppers to one. For extra spice, use 3 peppers or stir in more adobo sauce after shredding the chicken.***The chicken will have a lot of extra liquid, especially if you're serving it directly from the slow cooker. Use a pair of tongs to squeeze the chicken out a bit when you take it from the crock or bowl to help release some of the excess sauce.Nutritional information includes 1 tortilla, about ¼ cup of chicken tinga, 2 tablespoons red onion, 1 tablespoon cotija, and 1 tablespoon cilantroStore leftovers in an airtight container in the fridge for up to 4 days or freeze for up to 3 months. Reheat on the stovetop or in the microwave until hot.