Heat a large pot (with a lid) over medium heat. Once hot, add the oil and wait 30 seconds. Then add the onion and sauté 4-5 minutes or until lightly browned and translucent, stirring occasionally. Turn down heat as needed if browning too quickly.
Add garlic, mushrooms, bell pepper, and salt and stir. Sauté, stirring frequently, until softened and slightly caramelized ~5-7 minutes.
Add the oregano and red pepper flakes and stir until fragrant, about 1 minute.
Add the marinara and water and bring to a simmer. Break the pasta in half (disregard if using a smaller pasta shape) and add to the pot. Stir to break up any clumps.
Add optional greens at this time if desired. Then cover the pot, reduce heat to low, and simmer for 13 minutes, stirring twice.
Turn off the heat and let the pot stand, covered, for 2 minutes. Stir again to break up any remaining clumps of pasta (clumping should be minimal at this point). Uncover, taste, and adjust the seasonings as needed with more salt for overall flavor, oregano for herbal flavor, or red pepper flakes for heat.
Serve with fresh basil and vegan parmesan on top (optional). Store cooled leftovers in the refrigerator up to 2-3 days and reheat in the microwave or on the stovetop until hot, adding more water as needed to thin. Not freezer friendly.
*Nutrition information is a rough estimate calculated without optional ingredients.