Preheat the oven to 400 degrees F. Remove the mushroom stems, brush the caps with 1 tablespoon olive oil, and arrange them hollow sides up in a baking dish.
Cook the chicken sausage in a large skillet over medium-high heat for 5 to 7 minutes, breaking it into fine crumbles. Transfer the sausage to a mixing bowl.
Add the spinach and garlic to the same skillet and cook for 2 minutes, until the spinach wilts. Let it cool slightly, then press out any excess moisture.
Stir the drained cottage cheese, cooked spinach, 1/4 cup Parmesan, sun-dried tomatoes, Italian seasoning, 1/4 teaspoon salt, and black pepper into the sausage.
Season the mushroom caps with the remaining salt and divide the filling among them. Mix the panko, remaining Parmesan, and remaining olive oil, then sprinkle this mixture over the mushrooms.
Bake for 20 to 24 minutes, until the mushrooms are tender and the topping is golden. Rest for 5 minutes and finish with fresh basil before serving.