Heat a skillet over medium heat and add the ground turkey (or ground beef if using).
Cook, breaking the meat up with a fork, until it just loses its pink color, about 5–7 minutes.
Drain any excess fat from the cooked meat, then transfer the meat to the slow cooker.
Add the broken whole wheat spaghetti to the slow cooker and pour in the basil marinara sauce; stir to coat the pasta evenly.
Cover and cook on low for 2–3 hours (about 120–180 minutes) or until the spaghetti is al dente, stirring once if possible to prevent clumping.
When the pasta is done, transfer to a serving platter or bowls and sprinkle with the freshly grated Parmesan cheese.