Pre-heat the oven to 400°F. Place the plantain in a baking dish lined with aluminum foil and make a couple of 1/2-inch slits on its skin. Bake until completely cooked through, about 40 minutes. Remove from the oven, when cool enough to handle, peel and slice. Set aside.
Heat a comal, griddle or skillet over medium heat. Once hot, toast the ancho and guajillo chiles for about 30 to 45 seconds per side, until fragrant and lightly toasted. Place chiles in a saucepan along with the whole tomatoes, cover with water and set over medium-high heat. Simmer for 12 to 15 minutes, until the chiles are rehydrated and plumped up, and the tomatoes are cooked and mushy.
On the same comal, griddle or skillet, char the unpeeled garlic cloves and the onion slice, until completely charred and softened, about 8 to 10 minutes, flipping a couple of times in between. Set aside to cool. Peel the garlic when cool enough to handle.
On a small skillet set over medium heat, toast the cinnamon stick for a minute or two until fragrant, flipping once. Next, toast the cloves and peppercorns for a minute, moving them around the entire time. Toast the almonds for a couple of minutes, until lightly browned, as well as sesame seeds. Lastly, toast the oregano for 5 to 10 seconds.
As each ingredient is finished being toasted, place it in the jar of the blender: the cinnamon, garlic, onion, cloves, peppercorns, almonds, sesame seeds, and oregano. Add the rehydrated chiles, cooked tomatoes and 1 cup of their cooking broth, and the plantain to the blender, as well. Incorporate the raisins, sugar and 1 teaspoon salt, and puree at least for a couple minutes until completely smooth. If your blender is on the smaller side, puree it in batches.
Set a large casserole over medium-high heat and heat enough oil to have about 1/8-inch of depth. Season the chicken with the remaining teaspoon of salt. Once the oil is hot, brown the chicken pieces in batches, making sure to not crowd the casserole. Cook until they have created a crust on the skin and are easy to flip, about 3 minutes per side. Place the finished pieces in a large bowl.
Once you are done browning the chicken, reduce the heat to medium-low. Carefully, and using the casserole’s lid as a shield (there will be splatters), pour the mole sauce into the oil. Stir and cover with the lid, leaving it slightly open, and cook for about 6-7 minutes, stirring occasionally (still protecting yourself with the lid), until the sauce is very thick and seasoned. Add the chicken broth, chocolate pieces, and the browned chicken pieces, and cook for another 20 minutes. Add the chayote squash and green beans, give it a good stir, and cook until vegetables are cooked yet tender, another 10 minutes.
Serve with tortillas and/or rice.