Heat oil in nonstick skillet over medium heat. Add mushrooms, garlic, and green onions; cook 4 min. Or until tender, stirring occasionally. Add wine and cook until evaporated. Stir in salt, thyme and pepper. Remove from heat; cool.

Make a horizontal cut through center approximately 1/2 inch from each side, parallel to surface of steak, to form a pocket. Cut to, but not through opposite side. Spoon stuffing into pocket, spreading evenly. Close opening with toothpicks. Roast sirloin in a 350° oven on a rack in a shallow roasting pan for one hour or 20 min. Per pound. Remove steak from oven and let stand 10-15 min. Covered with foil tent. Remove toothpicks and carve into 1/2-inch thick slices.