Chop the sweet peppers and poblano chili pepper (remove seeds if desired). Add the chopped peppers, minced garlic, and chopped onion to the slow cooker. Stir everything together. Add in the chili powder, ground cumin, and chicken broth. Stir again and cook for 3-4 hours on high or until the broth is completely absorbed and the quinoa is cooked through. All slow cookers cook a little differently so make sure to occasionally check the dish to make sure the quinoa isn't burning or sticking all to the sides.
RECIPE UPDATE: I have had a few readers report a mushy consistency. It seems when readers are getting this result they are cooking it for too long and/or on low. I've never had a mushy consistency with this recipe which is why I specify in the instructions to cook it 3-4 hours on high (no options for cooking on low). For best results (as all slow cookers cook a little differently) check yours every hour and only cook on high for a maximum of 4 hours.