Preheat your oven to 300°F (150°C).
In a small bowl, combine the sea salt, black pepper, garlic powder, onion powder, and smoked paprika.
Rub the spice mixture thoroughly over all sides of the beef brisket to ensure even seasoning.
Place the brisket in a roasting pan or Dutch oven, cover tightly with foil or a lid, and roast for 3.5 hours until the meat is tender.
While the meat roasts, whisk together the tomato paste, apple cider vinegar, maple syrup, and yellow mustard in a small bowl to create the BBQ glaze.
Toss the Brussels sprouts with the olive oil and a pinch of salt, then roast on a separate sheet pan at 400°F (200°C) for the final 20 minutes of the brisket's cooking time.
Remove the brisket from the oven, discard the foil, and brush the BBQ glaze generously over the top of the meat.
Increase the oven heat to a broil and place the brisket back in for 3-5 minutes until the glaze is bubbling and slightly charred.
Allow the brisket to rest for at least 10 minutes before slicing thinly against the grain to serve.