Start by cooking your thick-cut bacon until it's perfectly crispy, then set it aside on paper towels to drain excess grease. While the bacon cools, slice your green tomatoes evenly; thicker slices help maintain their structure during frying.
In one bowl, combine cornmeal, flour, salt, black pepper, cayenne spice, and sugar for your dredging mixture. In another bowl, whisk together milk and an egg until smooth; this will be your wet batter.
Dip each slice of green tomato first into the wet batter and then coat generously with the dry mixture until well-covered. Set aside on a plate as you prepare to fry them up.
Heat oil in a large skillet over medium-high heat until shimmering but not smoking. Carefully add breaded tomato slices in batches, frying until golden brown on both sides; about 3-4 minutes per side should do it.
Spread Duke's mayonnaise on one side of each slice of white bread and layer with crispy lettuce, fried green tomatoes, and bacon as desired. Top with spicy brown mustard mixed with pickle juice and horseradish before finishing off with another slice of bread.
Slice each sandwich diagonally for easy handling and serve immediately while warm alongside your favorite sides like chips or pickles! Enjoy every crunchy bite of this mouthwatering creation!