Roughly chop the onion, reserving 1/4 for future use. Place large saucepot over high heat. Add in 1 tablespoon of vegetable oil and char the onion for 2-3 minutes. Add in tomatoes, chipotles, garlic, ancho, oregano, salt, orange juice, and cumin. Bring to a simmer and cook for 15 minutes. Once cooked, cool salsa, move to blender, and process until smooth.
Set oven to 275 deg F. In a large oven proof dutch oven or large pot, place over high heat. Add in one tablespoon of the oil and sear beef on all sides, ~8-10 minutes total.
Once beef is seared, add in enough salsa to just cover. Bake covered for 2.5-3 hours, then remove lid and cook until beef is very fork tender. Remove beef to cool, leaving the cooking liquid.
To make tacos: place a non stick griddle over medium heat. Dip a tortilla into the cooking liquid and place flat onto the heat. Top with a small handful of cheese, then meat. Fold over and cook 2-3 minutes a side or until just crisp. Some cheese will leak out, this is encouraged. Serve each taco with a bit of reserved onion (diced) and chopped cilantro... if you can wait long enough (like I clearly couldn't in the picture).