Heat the olive oil in a large skillet over medium heat. Add the sliced sausage and cook until browned on both sides, about 5 minutes.
Add the sliced onion and bell peppers to the skillet. Cook for 4 minutes until the vegetables start to soften.
Stir in the minced garlic, Italian seasoning, salt, and black pepper. Cook for 1 minute until fragrant.
Add the penne pasta, marinara sauce, and water to the skillet. Stir to combine and bring the mixture to a simmer.
Cover the skillet and cook for 12 to 15 minutes, stirring once halfway through, until the pasta is tender.
Remove the skillet from heat and stir in the grated parmesan cheese until melted.
Serve the pasta hot with fresh basil leaves scattered on top.