Remove stems from cilantro; tie together. Reserve leaves for sauce.
Place cilantro stems, chicken thighs, onion, garlic, cumin, chili powder, pepper, and salt into a slow cooker; add water.
Cook on Low until chicken is no longer pink in the centers and juices run clear, 8 to 10 hours. Transfer chicken to a plate and shred using 2 forks; set aside. Reserve 1 to 1 1/2 cups cooking liquid. Let onion and garlic cool slightly, about 5 minutes; dice and set aside.
Preheat the oven to 450 degrees F (230 degrees C).
Make sauce: Coat a baking sheet with cooking spray. Place tomatillos and jalapeño half, cut-sides down, onto the prepared baking sheet. Drizzle with canola oil.
Roast in the preheated oven for 25 minutes. Remove from the oven; wrap jalapeño in aluminum foil to let "sweat" for about 10 minutes. Remove skin from jalapeño.
Combine tomatillos, jalapeño, reserved cilantro leaves, green chiles, vinegar, cumin, chili powder, honey, pepper, and salt in the bowl of a food processor or blender; pulse until blended and smooth.
Pour tomatillo sauce into a large pot; add shredded chicken, diced onion and garlic, and beans. Stir in reserved cooking liquid. Let simmer over medium-low heat for 15 minutes.
