In a large pot, prepare pasta very al dente, cooking for about half of the time indicated on the package. Drain well and set aside.
In a bowl, combine turkey, ketchup, and onion. Mix well. Add frozen cauliflower and cheese sauce and gently mix. Transfer mixture to a slow cooker.
Add cooked pasta to the slow cooker and gently stir. Cover and cook on high for 3 to 4 hours or on low for 7 to 8 hours, until the turkey is fully cooked.
Add cheese wedges and scallions, and stir until evenly distributed.
If you like, season with salt and pepper, to taste. Dig in!