Fill up a large pot of water to a rapid boil.While waiting for the water to begin boiling, finely slice the onion and portabellamushrooms into thin slices, approximately ¼ inch thick. Set aside.
Once water begins to boil, add pasta, and cookaccording to packets instructions, until al-dente (typically 7-8 minutes). Immediatelydrain and set aside (make sure to reserve ¼ cup of cooked pasta water).
While pasta is boiling, add cooking spray or oilto a hot skillet, and gradually add in onion, mushroom, and garlic. Cover, and sautéfor about 7-10 minutes on medium-high, until the onions and the mushrooms havelightly browned.
Once the veggies have finished cooking, in thesame skillet, add the following ingredients into the mix: vegetable broth, pastawater, flour, olive oil, parmesan cheese, salt, pepper, oregano, Worcestershiresauce, and plain Greek yogurt. Mix untileverything is well combined (will look like a creamy, almost cheesy mixture). Raiseto boiling heat then reduce to medium and have the sauce simmer for about 10-15minutes, until everything has appeared to thicken. At this point, add in thespinach.
Once the sauce has thickened, add the cooked pasta,and gently stir until all the ingredients have been well combined. Enjoy!