Preheat your oven to 325°F (163°C). Generously season the chuck roast on both sides with kosher salt, freshly cracked black pepper, and taco seasoning.

Place the seasoned roast into a Dutch oven. Pour in the orange juice and beef stock, then add the quartered onions around the meat. Secure the lid tightly and transfer the pot to your preheated oven. Bake for about 3.5 to 4 hours until the meat is tender enough to shred easily with a fork.

Once cooked, carefully remove the roast from the oven. Using two forks, shred it into large chunks. If it's not falling apart yet, return it to the oven with the lid on for another 30 minutes until it's perfectly tender.

Raise your oven temperature to 425°F (218°C). On a baking sheet, toss the shredded meat with any remaining onions and sprinkle on some extra taco seasoning. Place it in the oven uncovered for 15-25 minutes until some parts start to caramelize and crisp up.

While your meat crisps up, whip up some fresh guacamole if you haven't already. For added flavor, char your tortillas over an open flame briefly. To assemble your tacos, spread a dollop of guacamole on each tortilla, pile on generous spoonfuls of shredded meat, and top off with your favorite salsa or other toppings.