In a large pot, heat 2 tablespoons of olive oil over medium heat. Add the diced yellow onion and sauté for about 4 minutes until it becomes translucent and soft, stirring occasionally.

Incorporate the minced garlic into the pot and cook for an additional 30 seconds, stirring constantly until the garlic is fragrant.

Pour in the marinara sauce and chicken broth to the pot along with the Italian seasoning. Stir everything together and bring the mixture to a gentle boil over medium-high heat.

Add the penne pasta to the boiling sauce, stirring well to ensure it is coated. Reduce the heat to medium-low, cover the pot, and simmer for about 10-12 minutes, stirring occasionally until the pasta is al dente.

Once the pasta is cooked, turn off the heat and stir in the shredded mozzarella and Parmesan cheese. Mix well until the cheeses are melted and creamy.

Serve your Cheesy One Pot Pasta immediately while it's warm and gooey. Garnish with fresh herbs or extra cheese if desired.