Preheat the oven to 180°C (350°F).
In a large oven-safe pot or deep baking dish, heat the olive oil over medium heat on the stove.
Add the chopped onion and minced garlic to the pot and sauté for 3-4 minutes until softened and fragrant.
Add the crushed tomatoes, vegetable broth, dried oregano, dried basil, salt, and black pepper to the pot. Stir to combine.
Add the penne pasta to the pot and stir to ensure the pasta is submerged in the liquid.
Bring the mixture to a gentle boil on the stove.
Remove the pot from heat and evenly arrange the sliced mozzarella cheese on top of the pasta mixture.
Cover the pot with a lid or aluminum foil and place it in the preheated oven.
Bake for 25 minutes or until the pasta is tender and the mozzarella is melted and bubbly.
Remove the pot from the oven and let it sit uncovered for 5 minutes.
Sprinkle the chopped fresh basil leaves over the pasta before serving.
Serve hot and enjoy your one pot pasta with tomato and mozzarella.