Preheat oven to 350 degrees Fahrenheit.
Remove thawed roast from packaging and lightly pat dry.
Lightly brush roast with cooking oil.
Roll the roast in the Omaha Steaks seasoning until all sides are covered.
Add cooking oil to large sauté or roasting pan and preheat until very hot (using proper ventilation) or, to cook outdoors, preheat grill to high.
Carefully place roast in pan or on grill and sear for 2-5 minutes on all sides until evenly browned.
Remove from the pan or grill and cool.
Spread foie gras pâté over top of roast, then sprinkle with truffles.
In a separate bowl, whisk egg and water to make an egg wash.
Roll thawed puff pastry dough into a rectangle approximately 3/16-inch thick and large enough to wrap around entire roast.
Flip roast and place lengthwise, pâté-side down, in center of pastry.
Fold pastry ends over and wrap around roast, sealing with egg wash and trimming off any excess pastry.
Transfer to a baking sheet seam-side down.
Brush puff pastry surface with the egg wash.
Bake Wellington for 40-55 minutes, or until the center reaches 125-130 degreesFahrenheit as per a meat thermometer. Let rest for 10 minutes after removing from oven.
Heat demi-glace in medium saucepan per package directions.
Carefully slice Wellington into 3/4-1"-thick slices and serve with mushroom demi-glace.