In a crockpot, combine chicken thighs, diced onion, minced garlic, diced tomatoes, chipotle peppers, cumin, oregano, smoked paprika, salt, and pepper. Stir to mix well.
Cover and cook on low for 6-8 hours or high for 3-4 hours, until the chicken is tender and easily shredded.
Once cooked, shred the chicken in the crockpot using two forks and stir to combine with the sauce.
For the avocado jalapeño crema, blend avocado, sour cream, jalapeño, lime juice, and salt in a food processor until smooth. Adjust seasoning to taste.
To assemble the tacos, warm the corn tortillas in a skillet over medium heat for about 30 seconds on each side.
Fill each tortilla with shredded chicken, top with shredded lettuce, diced tomatoes, and queso fresco. Drizzle with avocado jalapeño crema before serving.