Heat oven to 325°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray.
In 4-quart Dutch oven, heat olive oil and butter over medium-high heat until butter is melted. Add mushrooms and leeks; cook 4 to 6 minutes, stirring occasionally, until tender. Stir in remaining ingredients except bread cubes.
In large bowl, toss bread cubes with mushroom mixture. Spoon stuffing into baking dish. Cover with foil.
Bake 30 minutes; uncover and bake about 15 minutes longer or until top is golden brown and stuffing is hot in center (165°F).