Heat the olive oil in a large skillet over medium heat. Add the chopped mushrooms and cook for 6 to 8 minutes, stirring occasionally, until tender and their released liquid has evaporated. Stir in the sun-dried tomatoes and cook for 1 minute. Let the mixture cool slightly.
Heat the oven to 375°F. In a mixing bowl, combine the ground turkey, egg, breadcrumbs, milk, 1/4 cup of the Parmesan, oregano, garlic powder, salt, and black pepper. Add the cooled mushroom mixture and mix gently until evenly combined.
Shape the mixture into a loaf in a baking dish. Bake for 40 to 50 minutes, until the center reaches 165°F. Let the meatloaf rest for 5 minutes before slicing.
While the meatloaf bakes, bring the chicken broth to a boil in a small saucepan. Stir in the couscous, cover, and remove the pan from the heat. Let it stand for 5 minutes, then fluff with a fork and stir in the remaining Parmesan and parsley.
Serve the sliced meatloaf with the Parmesan couscous.