Prepare the marinade. Cut off the stems and remove the seeds from 2 guajillo chiles and 4 ancho chiles. Chop ½ a yellow onion, 5 cloves garlic, 2 bell peppers, and ⅓ cup pineapple. Set aside.
Heat a large frying pan to medium-high heat and drizzle with olive oil. Add the onion and cook for 2 minutes. Add in the garlic and chile peppers and cook for another 2 minutes.
Lower heat to low setting and pour in ¾ cup chicken stock and ¼ cup apple cider vinegar. Season with salt and cover with lid. Allow to simmer on low heat for 15-20 minutes.
Transfer everything from the pan into a blender. Add ½ cup worth of pineapple with a little bit of the pineapple juice into the blender along with 2 oz of achiote paste (about ⅔ of a block of el Yucateco achiote paste). Blend until fully liquified.
Place about 3 lbs worth of boneless chicken thighs in a bowl and marinate with the contents from the blender for at least 4 hours (preferably overnight) in a covered bowl placed in the refrigerator.
Preheat the oven to 350°F. After marinating, begin building your chicken tower. Cut up an entire pineapple and alternate while skewering by placing a few slices of chicken thigh on the skewer followed by a pineapple slice.
Place your tower on the bottom rack and bake for 1.5 - 2 hours or until chicken reaches an internal temperature of 165°F. Baste the tower every 30 minutes to prevent the chicken from drying out.
Remove from the oven and allow to cool for at least 10 minutes before cutting. Allow the pieces to collect in the roasting pan containing the drippings and toss to coat. Eat alone or serve on tacos with sour cream, salsa, hot sauce, and fresh cilantro for garnish. Enjoy!