Heat a large, heavy-bottomed pot over high heat. Pat the chicken pieces dry and sprinkle them generously with salt and pepper. Add the vegetable oil to the pot and sear the chicken in single layer batches, browning the chicken about 4 minutes each side, and then setting the chicken aside on a plate. Do not crowd the bottom of the pan and cook the chicken in batches until all of the chicken has been seared.
While the chicken is searing, heat a large saute pan over medium heat. Add the chiles de arbol, pasillas and anchos. Using dry heat, lightly toast the chiles in the pan until fragrant, about 3 minutes per side, being careful not to burn the chiles, shaking the pan often. Remove the chiles from the pan and set aside. Once the chiles have cooled, remove and discard the stems.
Add the peanuts, pepitas, coriander seeds, cumin seeds, peppercorns, cloves, bay leaves and cinnamon stick to the hot pan. Toast the nuts, seeds and spices in the dry pan until fragrant, about 4 minutes, being careful not to burn the spices. Remove from the pan and set aside with the dried chiles.
Once the chicken has finished searing, add the garlic, onions, jalapenos and orange slices to the pot. Stir well and season well with salt and pepper, using a wooden spoon to help scrape the brown bits from the bottom of the pot. Cook the vegetables until the onions begin to tenderize and soften, about 6 minutes, stirring often.
Add the chicken back to the pot with the onions. Add in the toasted chiles, spices, nuts and seeds. Stir in the brown sugar, dried fruit and Mexican chocolate. Pour the chicken stock and beer into the pot. Stir everything well and bring the pot to a boil over high heat. (At this point you can transfer the contents to an electric slow cooker, if preferred. Cook on medium heat for 6 to 8 hours). Reduce the pot to a simmer and cook, covered, over low heat for 2 hours, stirring occasionally to prevent the bottom of the pot from burning. The chicken is ready when it is fork tender.
Remove the chicken from the braising liquid into a bowl. Gently shred the meat with two forks. In small batches, blend the braising liquid and remaining cooked solids in a blender or food processor until smooth. The texture should resemble a loose puree. Add water or chicken stock as necessary. Repeat the process until all of the braise has been pureed. Combine the blended mole into a new pot, stirring and seasoning with salt, pepper and lime juice.
Add the desired amount of mole back to your pulled chicken (you may have a large amount of mole left over, which can be stored and frozen for up to 2 months).
To assemble, toast the slider buns cut-side down in a little butter on a griddle or pan to desired doneness. Spoon the chicken mole on the bottom half of the slider bun, top with a slice of avocado, some queso fresco and fresh cilantro leaves, then the top of half of the bun. Serve immediately.