Heat oil in a large stock pot over medium high heat. Season chicken on both sides with salt and pepper, sear on both sides. Remove from heat and set aside (doesn't need to be cooked through).
Add diced onion and garlic to the pot and saute until aromatic, no longer than one minute (being careful not to burn the garlic).
Add in the chicken stock and place the chicken back in the pot. Cover and let simmer for about 30 minutes or until the chicken is cooked through to 165 degrees F. Remove chicken once more; shred.
Whisk the masa harina a little at a time with the remaining stock and add in remaining ingredients including shredded chicken (excluding garnishes). Cook for about 30 minutes or until thickened; stirring occasionally making sure the bottom doesn't burn. Serve with your favorite garnishes. Enjoy!
Adapted from This Silly Girls Life