Place tomatillos cut side down, poblano peppers, anaheim peppers, jalapeños and unpeeled garlic cloves on a foil-lined large baking sheet. Place in the oven on broil for 10 minutes or until the tomatillos and peppers char.
Transfer the poblano and jalapeno peppers to a glass bowl and seal with plastic wrap to steam (leave the tomatillos and garlic on the baking sheet for now). After steaming for 10 minutes, remove skin and discard.
In a blender, combine the tomatillos and all their juices, peeled garlic cloves, assorted roasted and peeled peppers, cilantro, lime juice, cumin, salt, pepper and chicken stock. Blend the ingredients until they are well combined.
Season chicken thighs with 1 teaspoon kosher salt and 1 teaspoon ground black pepper.
In a large heavy bottom skillet or dutch oven, add 2 tablespoon olive oil and heat over medium high heat. Add the chicken and sear both sides until golden brown. Add the onions and saute for a few minutes before adding the mixture from the blender. Bring the mixture to a boil, reduce heat to medium and cover and simmer for 20-30 minutes until the chicken is cooked through and shreds easily with a fork. Taste and adjust salt and pepper as needed.
Serve in a bowl with tortilla chips on the side and tons cilantro on top.