In a large stockpot or Dutch oven over medium high heat, combine fettuccine, artichoke hearts, mushrooms, onion, garlic, basil, thyme, red pepper flakes and 4 1/2 cups water; season with salt and pepper, to taste.
Bring to a boil; reduce heat and simmer, uncovered, until pasta is cooked through and liquid has reduced, about 12-15 minutes.
Stir in spinach, Parmesan and butter until the spinach has wilted, about 2-3 minutes.