Set the slow cooker to high. Put the pork cubes in the slow cooker and season all over with the chipotle powder and some salt. Turn any pieces with the fat cap upright. Nestle in the garlic, cinnamon sticks and yellow onion. Pour the orange soda, vegetable oil and orange juice and zest over the pork. Cover and cook on high until super tender, about 4 hours.
Preheat the oven to broil.
Transfer the pork chunks to a baking sheet fat-side up. Let the liquid in the slow cooker settle so the fat is on the surface. Scoop off about 1/4 cup of the fat and drizzle over the pork chunks. Broil until the meat is crispy and the fat is bubbly, 1 to 2 minutes.
Serve with corn tortillas, Avocado Crema, diced white onion, cilantro and charred serrano if desired.
Zest and juice 2 of the limes and add to a food processor. Add the sour cream, cilantro, honey, cumin and avocado and process until smooth. If the mixture is too thick, thin it out with the juice of the remaining lime or some water. Season with salt and pepper. If not using the crema right away, cover with plastic wrap pressed on top to keep it from browning.