Garlic Butter Roasted Mushrooms

1 pound mushrooms
2 tablespoons capers, rinsed and chopped
3 large garlic cloves, minced
2 tablespoons vegetable oil
3 tablespoons unsalted butter, cut into pieces
2 teaspoons fresh lemon juice
1/4 cup chopped flat-leaf parsley

Preheat oven to 450°F with rack in middle. Toss mushrooms with capers, garlic, oil, 1/8 teaspoon salt and several grinds of pepper in a 1 1/2- to 2-qt shallow baking dish. Top with butter and roast, stirring occasionally, until mushrooms are tender and golden and bubbly garlic sauce forms below, 15 to 20 minutes. Stir in lemon juice and parsley. Serve immediately, with crusty bread on the side for swiping up the juices.