Rinse the corned beef off and let it rest for 20 minutes to come closer to room temperature. Heat the oven to 350 degrees F.
Pat the corned beef with paper towels if the surface is still wet. Rub on the mustard or other glaze, then sprinkle on the seasoning mix.
Wrap the roast in a tight-fitting layer of aluminum foil. Try to cover all the seams so leaks are minimal. Place the roast in a high-sided roasting pan or casserole dish.
Place the roast in the oven. Roast the meat for 1 hour per pound of meat. Open a corner of the foil, watching out for hot steam, and check the texture. Remove the meat when it becomes soft enough to easily penetrate with a fork.
Remove the fork and add any glaze, then place under the broiler for up to 20 minutes until the glaze has thickened and caramelized.