Heat a large skillet over medium heat and add the olive oil. Sprinkle the chicken thighs with salt and pepper. Add them to the skillet and sear until both sides are deeply golden brown, about 1-2 minutes per side.
Transfer the chicken to the slow cooker. Add the onion, pepper, garlic, tomatoes, and green chilies. Pour the soup mix in along with the chicken stock and stir.
Cook on low for 8-10 hours. Remove the chicken and shred it. (It will most likely fall apart.) Place chicken back in the pot.
Place the half-and-half in a shaker bottle and add the flour. Cover and shake for 30 seconds to create a slurry.
Stream the mixture into the slow cooker and stir. Cover and cook on high for 30 minutes.
Remove the lid and cook on low for 30 minutes, stirring occasionally.
Serve with lots of fixings, such as grated cheese, tortilla chips, avocado, jalapeño peppers, and cilantro.
