In a large pot or deep skillet, combine the dry spaghetti, sliced onion, minced garlic, sliced red bell pepper, sliced zucchini, diced tomatoes with juice, and vegetable broth.
Add olive oil, dried oregano, dried basil, red pepper flakes, salt, and black pepper to the pot.
Place the pot over medium-high heat and bring the mixture to a boil, stirring occasionally to prevent the pasta from sticking.
Once boiling, reduce heat to medium and simmer uncovered for about 10 to 12 minutes, stirring frequently, until the pasta is cooked al dente and most of the liquid has been absorbed.
Stir in the fresh baby spinach leaves and cook for an additional 2 minutes until the spinach is wilted.
Remove the pot from heat and stir in the chopped fresh basil leaves.
Taste and adjust seasoning with additional salt and pepper if needed.
Serve the one pot vegan pasta hot, garnished with extra fresh basil if desired.