Bring a large pot of salted water to a boil and cook the penne for 8 minutes until al dente, then drain.
While the pasta cooks, heat a large skillet over medium-high heat and cook the sausage for 5 minutes, breaking it into crumbles until browned and cooked through.
Add the marinara sauce, heavy cream, garlic powder, and red pepper flakes to the skillet and stir for 2 minutes until heated through.
Add the drained pasta, Parmesan cheese, and spinach to the skillet and toss for 1 minute until the spinach wilts and everything is coated.
Serve immediately with extra Parmesan if desired.