Heat the olive oil in a skillet over medium heat. Add the chopped mushrooms and cook, stirring occasionally, until they release their moisture and become tender. Let them cool slightly.

Set up an electric smoker according to the manufacturer’s instructions and preheat it to 250°F. Use a drip pan if your smoker requires one.

In a large mixing bowl, combine the ground beef, egg, breadcrumbs, milk, Swiss cheese, onion, Worcestershire sauce, salt, pepper, dried thyme, garlic powder, and cooled mushrooms. Mix gently just until combined.

Shape the mixture into a compact loaf and place it on a sheet of heavy-duty foil or in a small smoker-safe pan. Leave room around the loaf for smoke to circulate.

Smoke the meatloaf until the center reaches 160°F on an instant-read thermometer, checking the temperature in the thickest part. Transfer it to a cutting board and let it rest while you make the gravy.

Melt the butter in a saucepan over medium heat. Whisk in the flour and cook for about 1 minute, stirring constantly. Slowly whisk in the beef broth until smooth, then simmer until the gravy thickens.

Stir the parsley, rosemary, and fresh thyme into the gravy. Slice the rested meatloaf and serve with the warm herb gravy.