Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente. Drain and toss with 1 tablespoon of olive oil to prevent sticking. Set aside.
If your chicken breasts aren’t cooked yet, heat 1 tablespoon olive oil in a skillet over medium heat. Cook the chicken breasts until no longer pink inside, about 6-7 minutes per side depending on thickness. Let cool slightly, then shred the chicken using two forks.
In a large mixing bowl, combine the shredded chicken, marinara sauce, dried oregano, garlic powder, salt, and pepper. Stir until everything is well mixed and flavorful.
Add the cooked spaghetti to the chicken and sauce mixture. Toss gently to combine, making sure the noodles are coated evenly. Transfer this mixture to a greased 9x13 inch baking dish.
Sprinkle the shredded mozzarella and grated Parmesan cheese evenly over the top. Then scatter the chopped fresh basil leaves across the surface for a pop of fresh flavor.
Preheat your oven to 375°F (190°C). Bake the pasta casserole uncovered for 20-25 minutes, or until the cheese is melted, bubbly, and starting to turn golden brown.
Remove from the oven and let it rest for 5 minutes before serving. This allows the flavors to meld and makes it easier to portion out. Serve warm with a side salad or garlic bread for a complete meal.