Bring a large pot of salted water to a rolling boil. Add the penne pasta and cook 10 to 12 minutes until al dente. Reserve 1/2 cup pasta water, then drain the pasta in a colander.
While pasta cooks, heat olive oil in a large skillet over medium heat. Add minced garlic and sauté for about 1 minute until fragrant but not browned.
Add fresh spinach to the skillet with garlic. Stir frequently as spinach wilts, about 2 to 3 minutes.
Pour in heavy cream and stir to combine. Bring to a gentle simmer, then add grated Parmesan cheese. Stir until cheese melts and sauce thickens. Season with salt, pepper, and optional red pepper flakes.
Add drained penne pasta to the skillet with sauce. Toss gently to coat. If sauce is too thick, add reserved pasta water gradually to reach desired consistency.
Sprinkle cooked and crumbled turkey bacon over the pasta if using, right before serving.
Serve creamy garlic spinach penne in bowls or plates. Garnish with extra Parmesan or fresh herbs if desired.