To prepare potatoes, cut an 18 x 12-inch sheet of heavy-duty foil; lightly coat foil with cooking spray. Place potatoes and garlic in center of foil. Gather edges of foil to form a pouch; tightly seal edges. Pierce foil several times with a fork. Place pouch on grill rack; grill 30 minutes or until potatoes are tender, turning pouch occasionally.
Place potatoes and garlic in a large bowl; add milk, sour cream, butter, 3/4 teaspoon salt, and 1/2 teaspoon pepper. Mash with a potato masher to desired consistency; keep warm.
Preheat oven to 375°.
To prepare tofu, cut tofu lengthwise into 4 slices. Arrange tofu in a single layer on a foil-lined baking sheet coated with cooking spray. Lightly coat tofu with cooking spray. Bake at 375° 25 minutes or until tofu releases 3 or more tablespoons liquid. Cool slightly.
Lightly coat tofu with cooking spray; sprinkle with thyme and 1/4 teaspoon pepper. Place tofu on grill rack coated with cooking spray; grill 3 minutes on each side or until browned. Keep warm.
To prepare sauce, heat a large nonstick skillet coated with cooking spray over medium-high heat. Add shallots; sauté 1 minute. Add mushrooms; sauté 6 minutes or until moisture evaporates. Remove mushroom mixture from pan. Add wine to the pan. Bring to a boil, and cook until reduced to 3/4 cup (about 4 minutes).
Combine 1 tablespoon water and miso, stirring with a whisk. Add miso mixture, remaining water, mushroom mixture, 1/4 teaspoon salt, and 1/4 teaspoon pepper to pan. Bring to boil; cook until liquid is reduced to about 1 cup (about 4 minutes). Stir in parsley. Serve sauce with tofu and potatoes.