In a large deep skillet or wide pot, heat olive oil over medium heat.
Add the sliced onion and cook for 3-4 minutes until softened.
Add the sliced garlic, dried oregano, and crushed red pepper flakes. Cook for 1 minute until fragrant.
Add the dry spaghetti pasta, crushed tomatoes, vegetable broth, salt, and black pepper to the pot. Stir to combine and make sure the pasta is submerged in the liquid.
Bring the mixture to a boil over high heat.
Once boiling, reduce heat to medium-low and simmer uncovered, stirring frequently to prevent sticking, for 12-15 minutes or until the pasta is cooked al dente and the sauce has thickened.
During the last 2 minutes of cooking, stir in the chopped basil and baby spinach leaves until wilted.
Remove the pot from heat and stir in the grated Parmesan cheese until melted and combined.
Taste and adjust seasoning with additional salt and pepper if needed.
Serve immediately with extra Parmesan cheese sprinkled on top.