Preheat the oven to 400 degrees . Using the side of a knife, mash the garlic with a pinch salt to form a paste. In a bowl, combine the garlic paste, roasted red peppers, 1 teaspoon olive oil and the sage.
Brush the mushrooms with the remaining 2 teaspoons olive oil and stuff with the cheese. Arrange on a baking sheet, season with pepper and bake until the mushrooms are tender and the cheese is bubbling, about 15 minutes. Drain briefly on paper towels. Serve warm, topped with the red pepper relish.