Boil a large pot of salted water. Add spaghetti and cook according to package instructions until al dente, about 8-10 minutes. Drain and set aside.

In a skillet over medium heat, cook the ground beef or turkey until browned, breaking it apart with a wooden spoon, about 5-7 minutes.

Pour the marinara sauce into the skillet with the cooked meat and mix well. Let it simmer for about 5 minutes.

In a large mixing bowl, combine the drained spaghetti with the meat and sauce mixture and toss thoroughly.

Preheat your oven to 350°F (175°C). Fill each taco shell with the spaghetti mixture, packing it in without overstuffing.

Place the filled taco shells on a baking sheet and sprinkle shredded cheese on top.

Bake the tacos for 10 minutes or until the cheese is melted. Let cool slightly before serving.

Serve the spaghetti tacos with an array of toppings on the side.