Begin by gathering all your ingredients. In a large pot or a Dutch oven, combine the spaghetti, cherry tomatoes, onion, garlic, spinach, parsley, olive oil, salt, pepper, and red pepper flakes. Make sure everything is evenly distributed.
Add 4 cups of water to the pot. This will be the cooking liquid that will infuse the pasta with flavor. Stir gently to combine all the ingredients.
Place the pot over high heat and bring the mixture to a rolling boil. Keep an eye on it, as the bubbling action will start to soften the spaghetti.
Once boiling, reduce the heat to medium-low. You want a gentle simmer so that the pasta can cook without becoming mushy. Uncover the pot and let it cook for about 8 to 10 minutes.
Occasionally stir the pasta, ensuring that it doesn’t stick together. The spaghetti should begin to absorb the liquid as it cooks, thickening the sauce.
After about 8 minutes, check the consistency of the pasta. If it's tender and cooked through, it's time to finish. If not, continue simmering for a couple more minutes, adding a splash of water if needed.
Once the pasta has cooked to your liking, stir in the optional Parmesan. This will melt into the dish, adding a creamy texture and rich flavor.
Serve immediately, garnishing with extra Parmesan and a drizzle of olive oil if desired. Enjoy your homemade One Pot Pasta with Spinach!
