Step 1: Heat olive oil in a large skillet over medium heat. Add chopped onion and bell pepper and cook until softened, about 5-7 minutes. Add minced garlic and cook for another minute until fragrant.
Step 2: If desired, lightly brown the chicken pieces in the same skillet for 2-3 minutes per side to add extra flavor and depth, or skip this step for an even quicker prep.
Step 3: Transfer the cooked onion mixture (and browned chicken, if used) to a 6-quart or larger slow cooker.
Step 4: Add the diced sweet potatoes, diced tomatoes (undrained), tomato sauce, diced green chilies (undrained), and chicken broth to the slow cooker.
Step 5: Stir in the chili powder, ground cumin, smoked paprika, dried oregano, and cayenne pepper (if using). Season generously with salt and black pepper.
Step 6: Cover and cook on LOW for 7-9 hours or on HIGH for 4-6 hours, or until the chicken is cooked through and easily shreds, and the sweet potatoes are tender.
Step 7: Carefully remove the chicken from the slow cooker and shred it using two forks. Return the shredded chicken to the slow cooker and stir to combine.
Step 8: Taste the chili and adjust seasonings as needed. If the chili is too thin, you can mash some of the sweet potatoes against the side of the slow cooker to thicken it slightly, or remove a cup of liquid, whisk in 1 tbsp cornstarch, and return to the slow cooker for the last 30 minutes.
Step 9: Ladle the warm slow cooker chicken and sweet potato chili into bowls. Garnish with your favorite toppings such as shredded cheese, a dollop of sour cream, fresh cilantro, sliced avocado, or crushed tortilla chips. Serve hot and enjoy!