Mushroom Stuffed Beef Rouladen

Name: Mushroom Stuffed Beef Rouladen
Ingredients: 3 tablespoons vegetable oil, divided; 2 cloves garlic, chopped; 1 onion, diced; 1 pound assorted mushrooms (brown, Portobello, button, etc.), thinly sliced; 1 teaspoon dried thyme; Salt and pepper to taste; 1 egg, beaten; ¼ cup bread crumbs; 8 (3 ounce) pieces shoulder steak, pounded thin; ¼ cup dry red wine; 2 ½ cups beef stock; ¼ cup all-purpose flour; 1 tablespoon Dijon mustard