Bring a large pot of salted water to a boil and cook the spaghetti, according to the package instructions, until al dente. Drain the spaghetti and drizzle a teaspoon of olive oil atop; toss the pasta (this will help it from sticking) and set aside.
In a large pan, heat 3 tablespoons of butter over high heat. Add the mushrooms and sauté, stirring constantly, for 3 to 5 minutes or until al dente and golden. Season to taste with salt and a few turns of freshly ground pepper and then transfer to a medium bowl.
Place the pan over medium-high heat, add 2 tablespoons of butter, and fry the sage for about 30 seconds or until crisp and golden but not dark. Transfer the sage to a plate. Add the orange juice and deglaze the pan, using a spatula to scrape any bits and pieces off the bottom. Add the pasta and mushrooms to the pan, stir to combine, and season to taste with salt, pepper, and orange zest. Sprinkle with grated Parmesan-Reggiano, crispy sage and serve immediately.