Cook the penne pasta in salted water according to package directions. Reserve 1/2 cup of the pasta water and drain the rest.
In a large skillet, heat olive oil over medium heat. Sauté garlic and chopped onion until softened.
Add the peas and cook for 2–3 minutes, then add the reserved pasta water and stir in the cream cheese.
Season with salt and pepper, then add the cooked penne pasta and stir until well coated.
Serve warm, topped with fresh basil leaves.