Combine the onion, butternut squash, garlic, cumin, paprika, salt, tomatoes, broth, and quinoa in the base of a 6-quart slow cooker, stirring to combine.
Cover and cook for 4 hours on high or 6 hours on low, or until the onions and butternut squash are very tender and cooked through.
Uncover, add the kale, cover, and cook on high for the kale to wilt about 15-30 minutes.
Uncover and add the vinegar, stirring to combine. Taste and add additional salt or vinegar if you like.