To make the mole sauce, soak the chiles in 1 1/4 cups water for 15 minutes. Drain well and discard the soaking liquid.
Heat the oil in a large heavy saucepan over medium heat. Add the onions and garlic and saute until translucent, 5 minutes. Transfer to a blender with the chiles, chocolate, chicken broth, peanut butter, sugar, oregano and tostadas and blend until very smooth. Transfer the sauce to a saucepan and bring to a boil over high heat. Reduce the heat to medium, cover and simmer for 20 minutes.
Season with salt and pepper. Add the rotisserie chicken pieces and stir to combine.
Recipe courtesy of Marcela Valladolid