In a large skillet over medium heat, add the canola oil and salted butter. Once the butter has melted and begins to bubble, add the sliced onions. Cook for about 3 minutes until they start to soften.

Add the sliced mushrooms to the skillet and sauté them together with the onions for an additional 4 minutes until both ingredients are mostly softened and fragrant.

Stir in the Dijon mustard, water, Worcestershire sauce, salt, and pepper. Cook this mixture for another 4-5 minutes to reduce the sauce.

Remove from heat and set aside.

While the mushroom mixture cools slightly, preheat your grill to medium-high heat, aiming for a temperature between 375-400 degrees Fahrenheit.

In a large mixing bowl, combine the ground beef with the seasoning salt, Worcestershire sauce, pepper, and garlic powder. Mix gently until just combined, being careful not to overwork the meat.

Divide the mixture into 4 equal pieces and shape them into patties slightly larger than the hamburger buns you will use.

Place the patties on the grill and cook for 4-6 minutes on each side, depending on your desired level of doneness.

In the last 2-3 minutes of grilling, place a slice or two of Swiss cheese on each patty, allowing it to melt beautifully over the top.

Once cooked, remove the patties from the grill. Assemble the burgers by placing a patty on a bun and topping it with a generous spoonful of the mushroom mixture.

Add any additional condiments you desire and enjoy!