Preheat the oven to 375 degrees. Coat a baking dish with cooking spray then add a cup of water to the baking dish.
Whisk the apricot jam, Dijon mustard, grainy mustard, and brown sugar together until well combined.
Remove the pre-cooked corned beef out of the package and place it in the prepared baking dish. Smother the corned beef with most of the apricot sauce, leaving the remaining sauce for dipping. Place into the oven and bake for 30 minutes.
Side Note: If you can't find a pre-cooked corned beef, simply following the packaged directions for boiling OR bake in the oven. To do bake, preheat the oven to 350 degrees. Layer a large piece of tin foil in a baking pan then place the corned beef fat side up on top of the foil. Smother in the sauce then wrap the corned beef with foil so that space is left in between the corned beef and the tin foil. Place into the oven and bake for 2 hours. Open the foil and broil the corned beef for 2-3 minutes, until the top is bubbly and lightly browned. Watch carefully so it doesn't burn.
Remove the corned beef from the oven and place it onto a cutting board. Let the corned beef rest for at least 10 minutes before slicing across the grain of the meat. Serve with the reserved apricot mustard sauce. Enjoy!