Toss 1 small leek (halved lengthwise, dark green top discarded) and 8 ounces torn oyster mushrooms with olive oil; season with salt and pepper. Grill over medium-high heat, flipping, until charred, 6 to 8 minutes. Slice the leeks and the mushrooms. Cook 1 cup couscous as the label directs; fluff with a fork. Stir in the grilled vegetables and 1/4 cup chopped parsley. Top with toasted sliced almonds.