Preheat the oven to 250 degrees.
In a skillet, toast the coriander seeds until fragrant, about 3-5 minutes. Then, remove them from the heat and crush them in a food processor or mortar and pestle.
In a mixing bowl, whisk together all of the dry rub ingredients: cacao powder, salt, cumin, paprika, chili powder and crushed coriander seeds. Make sure they are all combined.
Pat the meat dry with a paper towel. Whether the meat is already cut into chunks or if it's one big roast, coat the meat thoroughly in the dry rub mixture. If you have any of the dry rub leftover, reserve it for later.
Season a dutch oven with oil and heat on medium high, until shimmering. Whether you're using a roast or pre-cut meat, sear the meat on all sides until crisp, about 1-2 minutes. Once all sides are crisp, remove the meat from the dutch oven, but keep the oil in the pot.
Adjust the heat to medium, then add the onion to the pot and sauté until slightly caramelized and soft, 3-5 minutes. Add the garlic and and sauté for 2 minutes, until fragrant.
Adjust the heat to low, then add all of the liquid and citrus zest into the dutch oven. Mix the liquids to fully combine and mix them with the onions and garlic.
Re-coat the meat with any leftover dry rub, then place it on top of the onion and garlic mixture.
Put the lid onto the dutch oven and place it into the oven for 1-2 hours.
After 1-2 hours, cut the meat into pieces and put it back in. Check on it again in another 2 hours.
The cut pieces of meat should be more tender. Use a fork and knife to shred the meat, going with the grain The grain is the line going through the meat. You want to cut with it, allowing for the meat to tear much more easily than if you were tearing against it. Your meat won't tear if you go against the grain, instead, you'll have to slice through it.
Put the shred meat back into the dutch oven, then pour 1 cup of water in and mix it all together. Let the meat cook for 1-2 more hours, until done.
15-20 minutes before the meat is done, season a sauté pan with oil over medium high heat. Add the sliced peppers and tomatillos and sauté until charred, a little crunchy but also tender. Remove them from the heat.
Flat cut side down, place the citrus slices onto the hot skillet over medium heat. Let them char for 2-3 minutes, until you can see the caramelization on the surface when you flip it. Once the citrus is charred, remove from the heat.
If desired (or if you're low maintenance like me,) serve the beef in the dutch oven and top with the bell peppers, tomatillos and charred citrus. Serve the beef with rice, on tortillas, and topped with some cilantro for a bright flavor boost. Serve immediately, or eat in an hour. It tastes even better at room temp. If storing, seal in an air tight container and put it in the fridge.