Using saute function on multiple purpose cooker (Instant Pot), saute onion, garlic in 1 tbsp. oil until translucent and aromatic. Add chicken breasts on top. Season with with chili powder, cumin, oregano, and salt/pepper.
Add in chili en adobo, canned tomatoes, and 5 ½ cups of chicken broth. Put lid on multicooker and set to high pressure for 20 minutes.
Meanwhile, mix together masa harina, shredded cheese, ½ cup broth, and 3 tbsp. oil in a mixing bowl until combined.
Once multicooker is completed, release pressure manually for quick release. Remove chicken breast and shred with two forks, add back to soup. Switch to saute function. Once soup is boiling, drop about spoonfuls of (about 1 tablespoon each) of masa mixture into the boiling soup. Once all dumplings are in the soup, turn off saute function and allow to simmer for 5-10 minutes or until a toothpick is inserted into the dumpling comes out clean.
Serve with toppings.