Prepare all sandwich ingredients. Slice onion and tomato, mix coleslaw shavings with your preferred dressing, lay out bread, and have your meat and cheese at the ready.
Heat griddle to 350°F or a non-stick pan to medium heat. Coat with cooking spray.
Put onion, tomatoes, and turkey on griddle or pan to heat. Flip 1-2 times and let sizzle for 5-6 minutes (or until light browning on each side).
While the onion, tomatoes, and turkey warm, spray griddle or another pan again with cooking spray, butter each side of the bread and place one slice of bread on the pan. Ensure the part of your bread being toasted is the outside so when you fold your sandwich, it's nice and crispy.
Place a slice of cheese on each slice of bread. Let melt.
Start to layer your sandwich. Put sautéed onions on one piece of bread and sautéed tomato slices on the other. Divide warmed turkey evenly on each piece of bread.
Top one side of the sandwich with prepared coleslaw. Add more dressing if needed. Top with another slice of butter bread.
Using a spatula, flip the sandwich so the fresh side of the bread gets grilled.
Once warm and golden brown, remove from heat, cut in half, and enjoy immediately. Grab the napkins because this is a finger licker.