Remove ground beef from the fridge 15–20 minutes before cooking to bring it closer to room temperature. In a large mixing bowl, combine the ground beef, sea salt, black pepper, garlic powder, and barbecue sauce. Mix with your hands until the seasonings are evenly distributed — do not overmix or the patties will be dense.

Place about 3 oz (85g) of the seasoned beef mixture into the bottom of a stuffed burger press (or flatten it on a sheet of plastic wrap). Spread approximately 2 tablespoons of chopped smoked brisket in the centre, leaving a ½-inch (1cm) border around the edge.

Place another 3 oz (85g) of beef on top of the brisket and press firmly to seal the edges. Repeat until you have 8 stuffed patties. While forming the patties, heat a 12-inch cast-iron skillet over medium-high heat with 1½ tablespoons (22ml) canola oil. When the oil shimmers and is just beginning to smoke, carefully place 3–4 patties in the skillet — do not crowd the pan. Sear for 3–4 minutes per side until a dark crust forms and the internal temperature reaches 160°F (71°C). Transfer to a wire rack to rest.

Let the patties rest for 3–5 minutes. While they rest, split the hamburger buns and toast them cut-side down in the skillet for about 30 seconds until golden. Spread a thin layer of barbecue sauce on the bottom bun, place the patty on top, add 1–2 rings of red onion, then finish with about 2 tablespoons of coleslaw. Press the top bun down gently and serve immediately.