Heat the oil in a large pot or Dutch oven over medium-high heat. Once the oil is melted, add the vegan sausage. Cook, stirring or flipping occasionally, until the sausage is heated through and starts to crisp on the edges, 4 to 5 minutes. Remove the sausage from the pan and set aside.

In the same pot, add the onion, bell peppers, and tomatoes. Cook, stirring occasionally, until most the onions become translucent, and the peppers and tomatoes are tender, 6 to 8 minutes. Add the garlic and cook another 1 to 2 minutes. Sprinkle the mixture with the flour and mix well, making sure there are no clumps.

Slowly pour in the broth and milk, stirring to ensure there are no clumps. Add the pasta and parsley. Season with the cajun seasoning and nutritional yeast; stir well. Increase the heat to high and bring to a boil. Reduce the heat to low, cover, and simmer until the noodles are tender, 12 to 15 minutes. Remove the lid, stir in the vegan parmesan, and continue to stir until it’s melted throughout. Taste and adjust seasonings, adding salt and pepper, if necessary. Let the pasta cool about 5 minutes before serving. Garnish with green onion and a sprinkle of vegan parmesan, and enjoy!