Fully cook the turkey using method of choice. If pressed for time, I use an Instant Pot or pressure cooker, but you can grill, smoke, or roast the turkey, as well. Make sure the internal temperature of the turkey reaches 165-degrees.
After fully cooking the turkey, let the turkey return to room temperature or cooler.
Coarsely dice a red onion and grind the turkey meat and red onion together into a large bowl. For grinding the meat, I use a 1/2-HP brute-of-a-grinder made by Cabela's, but you can also use KitchenAid's food grinding attachment. https://www.amazon.com/KitchenAid-FGA-Food-Grinder-Attachment/dp/B00004SGFH
Add approximately 1 tbsp. of Fat Pants, 1 tbsp. of salt, and 1 tsp. of pepper to the bowl of ground turkey/onion. Mix well with clean hands or large spoon.
Refrigerate the (dry) turkey salad until you are ready to serve it, and then mix in mayonnaise to get to the consistency you prefer.
Serve the turkey salad on your bread of choice. You can also add a slice of sharp cheddar, lettuce, sliced red peppers, or a slice of tomato with the sandwich.