Place 2/3 of the chopped sweet potato, onion, garlic, chipotle pepper, paprika, cumin, vegetable broth, vinegar, and soy sauce in a slow cooker. Cook on high for 3-4 hours or on low for 6-8 hours. One hour before serving, preheat oven to 400 degrees F. Toss remaining sweet potato chunks in oil and spread on a baking sheet. Bake in oven for about 40 minutes, stirring a few times while cooking