Roast Beef Subs with Balsamic Onions and Brie Cheese

Stir beef, Worcestershire sauce, and Montreal steak seasoning together in a bowl. Marinate beef while preparing other items.

Heat olive oil in skillet over high heat. Cook and stir onions in hot oil until golden brown, about 15 minutes; add balsamic vinegar, salt, and black pepper. Reduce heat to low and cook the onion mixture at a simmer until there is little liquid remaining and the mixture is syrup-like in texture, about 10 minutes.

Preheat an outdoor grill to 400 degrees F (200 degrees C) and lightly oil the grate.

Remove steak pieces from the marinade and shake off excess. Discard the remaining marinade.

Combine beef and canola oil in a bowl and toss to coat.

Preheat oven to 200 degrees F (95 degrees C).

Cook the beef slices on the hot grill, turning frequently, until they start to firm and are reddish-pink and juicy in the center, 4 to 6 minutes per side. An instant-read thermometer inserted into the center should read 130 degrees F (54 degrees C).

Arrange rolls onto a baking sheet. Spoon onions into the bottom of the sandwich rolls; add beef. Top beef with Brie cheese.

Heat in preheated oven until the cheese melts, about 5 minutes.