Preheat your oven to 150°C (300°F). Cut the pork shoulder into large chunks. Season generously with salt and black pepper.
In a large ovenproof pot or Dutch oven, heat olive oil over medium-high heat. Sear the pork pieces until browned on all sides, about 10 minutes. Remove and set aside.
Lower the heat to medium. Add chopped onion and minced garlic to the pot, cooking until the onions are soft and translucent, about 5 minutes.
Stir in the cumin seeds and dried ancho chillies. Cook for an additional 2 minutes until the spices are fragrant.
Add the canned chopped tomatoes, bay leaves, the juice and zest of the orange, and the juice of the lime. Bring to a simmer.
Return the pork to the pot, cover, and place in the oven. Cook for 3-4 hours, or until the pork is tender and easily pulls apart with a fork.
Remove the pork from the pot and shred with two forks. If desired, reduce the remaining sauce on the stove to thicken, then mix with the shredded pork before serving.