Preheat oven to 425°F. Poke holes all around each sweet potato with a fork.
Cover in foil and bake for 45-60 minutes, until tender and easy to cut through. (The bigger the sweet potatoes, the longer they'll need to bake.)
Remove the sweet potatoes from the oven, remove the foil and set aside until cool enough to handle.
To make the chicken
In a dutch oven or pot, add chicken, onion, garlic, salt and bay leaf. Add enough water to cover the chicken and bring to a boil over high heat. Reduce the heat to simmer and cook for 25 minutes, until chicken is tender and can be shredded with a fork.
Remove the chicken from the pot with a slotted spoon and transfer to a plate or cutting board. Shred the chicken, season with salt and set aside.
Heat the enchilada sauce and black beans on the stove or in the microwave, until hot.
Cut the tops of each sweet potato into an oblong shape. (See the video in the recipe post for a visual example.) Scoop out a little of the inside so that you can fill it in with the toppings.
Fill each sweet potato with shredded chicken, enchilada sauce, black beans, avocados, cilantro, cotija cheese and sour cream.