Nestle the fettuccine nests into the center of the skillet, keeping everything in a single layer so it cooks evenly
Add the red onion, garlic, cherry tomatoes, spinach, and Italian seasoning directly into the pan, spreading everything into an even layer. Drizzle olive oil over all the ingredients.
Pour the vegetable stock and heavy cream over the pasta, then spoon marinara sauce directly onto each nest.
Cover tightly with a lid and let it simmer for about 10 minutes on medium low heat.
Once the pasta has softened, uncover and give everything a good mix to combine the sauce and vegetables. Add the parmesan cheese and stir until melted and creamy. If you like it more saucy, add a splash more vegetable stock here.
The dish is done when the noodles are tender and the sauce is thick, creamy, and coating everything beautifully.
Serve immediately and top with shrimp, salmon, or chicken if you want to add more protein.