Preheat the oven to 350 degrees F (175 degrees C).
Bring a large pot of lightly salted water to a boil. Cook gnocchi in the boiling water until they float to the top, 2 to 4 minutes.
Meanwhile, heat a large skillet over medium-high heat. Cook and stir ground turkey in the hot skillet until browned and crumbly, about 5 minutes, making sure not to overcook as meat will continue to brown in the oven. Stir in marinara sauce; remove from heat.
Transfer cooked gnocchi to a 9-inch square baking dish using a slotted spoon. Top with meat sauce. Sprinkle Cheddar cheese on top.
Bake in the preheated oven until cheese begins to brown, 25 to 35 minutes. Serve with sour cream on the side.