Thoroughly rinse produce and pat dry. Cut onion and tomatoes into a dice. Stem Portobello mushrooms and cut stem into a dice. Using a spoon, gently remove mushroom gills from cap. Cut caps into 1/2" pieces. Stem and dice parsley.

Bring a medium pot of lightly salted water to a boil and put a colander in the sink. Once water is boiling, add the pasta. Cook for 8-12 minutes, until al dente and drain. Gluten-free pasta can stick together as it cooks, so be sure to stir with a slotted spoon, if necessary, to break up any clumps.

While the pasta is cooking, prepare the sauce. In a mixing bowl, whisk together vegetable bouillon cube and 1/2 cup warm water until cube is entirely dissolved. Line a medium pan with a thin layer of bouillon liquid. Add onion and sauté over medium heat until translucent (this technique is called “deglazing”). Add mushrooms, stirring occasionally until all the liquid has been absorbed, adding a splash of vegetable stock as needed to deglaze the pan.

Adjust heat to low-medium and stir in tomatoes, pumpkin, tomato sauce, and Italian seasoning and let simmer 5-10 minutes. Season with salt and pepper to taste.

Arrange a pile of spaghetti on to the plate, twisting as you go to build height. Ladle of the sauce atop the spaghetti. Garnish with fresh parsley and a crack of fresh black pepper.