Set the oven to broil.
Place tomatillos, poblano peppers, jalapeno, and unpeeled garlic cloves onto a sheet pan.
Broil on the top rack of the oven, turning ingredients occasionally, for 15-20 minutes, or until skin is blackened in spots on all sides. (Note: You can remove items individually as they are ready. Remove garlic first so that it doesn't burn.)
Peel the skin from the roasted garlic cloves, and set the peeled cloves aside. Place the roasted poblanos and jalapenos into a sealable ziploc bag. Let cool, remove skin and seeds from peppers, and dice.
Put diced peppers, tomatillos and garlic cloves into a blender. Add chicken broth, 1/2 cup cilantro, salt, cumin, and onion powder and blend until combined. (You should end up with about 4 cups of sauce. If you have less, you can add some additional broth).
Pour blended mixture into a slow cooker. Add shredded rotisserie chicken and drained beans. Cook on low for several hours until ready to serve.
Serve topped with additional cilantro and cheese, if desired.