Preheat the oven to 425 degrees F. Bring a large pot of water to a boil.
Add the gnocchi to the boiling water and cook according to the package directions; drain, reserving ¼ cup of the cooking liquid.
Meanwhile, heat the oil in a large nonstick cast iron skillet over medium-high heat. Add the onions, garlic, and carrots and cook, stirring occasionally, until soft, about 5 minutes. Add the dried fennel, ground beef, and pork and cook, stirring occasionally, until the meat is cooked through, about 10 to 12 minutes. Remove from the heat and season with salt and pepper.
Add the gnocchi, reserved cooking liquid, and marinara sauce to the skillet and stir to combine. Add the parmesan and stir.
Sprinkle with the mozzarella. Bake on the top oven rack until hot and bubbling and the cheese turns golden, about 15 minutes. Remove from the oven and let sit for 5 minutes.
Top with fresh basil, serve, and enjoy!