Using a casserole pan, sauté the pancetta until it crisp.
Add the mushrooms and oregano, then stir together. Cook until mushroom is soft.
Add the diced tomatoes, spinach, chili flakes, and freshly cracked black pepper.
Stir and bring to a boil.
Reduce heat and cover partially with the lid. Simmer for 20 minutes with gradual stirring to break down the spinach.
Using another pot with salted boiling water, cook the spaghetti noodles until al dente. Reserve a cup of pasta water then drain the spaghetti.
Transfer the cooked spaghetti to the cooked sauce and add a little of the reserved pasta water.
While still on the heat, stir for 30 seconds until everything is combined.
Serve with grated parmesan cheese on top if preferred.