Place the achiote paste in a medium-size bowl. Add juice from a fresh orange, vinegar and mix all ingredients until completely diluted - no chunks.

In another bowl, place a plastic bag. Add the chicken legs and half of the achiote mix. Then, rotate the bag until legs are covered entirely by the mix. Add half of the onions, then close the bag and make sure to remove its air.

Repeat the plastic bag process for the chicken thighs.

Preheat the griddle at medium heat for 5 minutes. Add butter, and spread it on the surface. Put the chicken legs and thighs and cook turning pieces around from time to time. Cooking takes about 15 minutes at 176 degrees.