Boil a large pot of salted water. Cook spaghetti according to package directions until al dente, about 8-10 minutes. Reserve ½ cup of pasta water and drain spaghetti.

In a large skillet, cook thick-cut bacon over medium heat until crispy, about 5-7 minutes. Transfer to a paper towel-lined plate.

Add sliced mushrooms to the skillet with bacon fat, increasing heat to medium-high. Sauté until browned and tender, about 5-7 minutes.

Stir in minced garlic with mushrooms and cook for another minute until fragrant. Do not burn.

Reduce heat to medium, add pumpkin puree, thyme, smoked paprika, nutmeg, salt, and pepper. Stir until combined and heated through, about 2-3 minutes.

Pour in heavy cream and grated Parmesan cheese, stirring gently until melted and well combined. Simmer for 2-3 minutes until sauce thickens.

Add cooked spaghetti to the skillet, tossing to coat in the creamy pumpkin sauce. Stir in reserved pasta water as needed for desired consistency.

Serve hot, topped with crumbled crispy bacon and chopped fresh parsley. Add extra Parmesan cheese if desired.