Preheat the oven: preheat the oven to 180°C / 350-375°F / Gas Mark 4-5.
Dry rub: add the mustard powder, garlic powder, onion powder, paprika, cayenne pepper, salt and pepper to a jug and use a mini whisk to combine. Then set aside.
Brisket: remove brisket from packaging, rinse then pat dry with paper towel. Transfer to dry, clean chopping board.
Rub into brisket: sprinkle half of the dry rub of the top side of the brisket and then use your hands to massage this into the meat. Then flip the brisket to the other side and sprinkle the remainder of the dry rub over the top. Massage the rub into this side of the meat also.
Oven bake: cover a baking tray with a layer of tin foil and give it a spray with cooking oil. Then place the dry rub covered brisket into the middle of the tray. Pour water into the base of the tray so that it sits around the brisket and sides but not covering it. Bake for 3 ½ hours, removing from the oven every hour to top up the water.
Grill/broil: use oven mits to remove the cooked brisket from the oven and place the baking tray on a heatproof surface. Change the oven setting to grill at 200°C 392°F6.
Sauce: use 2 pairs of kitchen tongs to transfer the cooked brisket to a silicon mat above a baking tray and rack. Use a pastry brush to liberally coat the top and sides brisket with the barbecue sauce. Place the brisket into the oven on the top shelf and grill it for 10 mins. Then remove, rebaste with sauce and grill for a further 10 minutes (Total grill time is 2 x 10 mins = 20 minutes).
Pull: remove the baking tray from the oven and let it sit for 3-4 minutes. Then use 2 pairs of tongs to transfer it to a clean chopping board. Hold a fork in each hand and use the forks to shred the meat (pull your hands away from each other). Repeat to pull the entire piece of brisket.
Sauce (optional): add the pulled brisket to a bowl, pour in the remaining sauce and stir till this is combined.
Serve: use the pulled beef brisket as a taco filling, for burgers, sandwiches grilled cheese filling or whatever takes your fancy.