Place the pepperoni on a hot grill, cut side down. Grill for 3 minutes per side. Remove from the grill and slice into 1/4-inch thick slices. Heat the oil in a large skillet over medium heat. Add the onions and cook, stirring, for 6 minutes. Add the mushrooms and cook, stirring, until soft, about 5 minutes. Season with salt and pepper. Add the grilled pepperoni, garlic, basil and spinach. Cook, stirring, for 3 minutes or until spinach has begun to wilt. Add the beef broth and bring to a boil. Reduce the heat to a simmer. Add the heavy cream and bring back up to a boil. Reduce the heat and simmer for 5 minutes. Add the Parmesan cheese and mix well. Add the pasta and toss well. Season with salt and pepper.