In a large non-stick pan, saute onion in oil until translucent and slightly brown on edges. Add garlic, cumin, and chili powder to the onion and cook for 1-2 minutes.
Add onion and garlic mixture to slow cooker along with chicken breasts, chicken broth, salt, pepper, oregano, green chilis, pumpkin, and beans.
Cook on low for 6-8 hours or high for 4 hours. Before serving, remove the chicken and chop into bite-size pieces and return to the chili OR roughly shred with 2 forks in the slow cooker. Serve warm with your favorite toppings!