Preheat your oven to 300°F and prepare a small baking dish.
In a small bowl, combine the smoked paprika, garlic powder, onion powder, sea salt, and black pepper to create a dry rub.
Apply the spice rub evenly over all sides of the beef brisket, pressing it into the meat.
Place the brisket in the baking dish, cover tightly with foil, and roast for 3 to 4 hours until the meat is tender and easily shreds with a fork.
While the brisket rests, heat the olive oil in a skillet over medium-low heat.
Add the thinly sliced yellow onion to the skillet and cook slowly for 20 minutes, stirring occasionally, until deeply golden and caramelized.
Stir in the balsamic vinegar to deglaze the pan and coat the onions, then remove from heat.
Steam or roast the asparagus spears for 5 minutes until tender-crisp and bright green.
Slice the brisket against the grain and serve topped with the caramelized onions alongside the asparagus.