Place Great Northern beans into a large container and cover with several inches of cool water; let stand 8 hours to overnight. Drain and rinse beans.
Place beans, chicken, onion, chicken broth, jalapeno pepper, cumin, oregano, and garlic powder in a slow cooker.
Cook on High for 4 hours or on Low for 8 hours. Remove chicken breasts from the chili and place on a work surface; shred chicken breasts with a fork and mix back into chili.
Spoon chili into 4 bowls; top each serving with 1/4 of the chopped tomato, 1 ounce Mexican cheese blend, and 1 tablespoon chopped cilantro.
