Preheat oven to 400°F.
Wrap a baking sheet with foil and place the bacon on it. Bake until crisp, about 10 to 15 minutes. Drain on paper towels. Set aside.
Whisk together the flour, cornmeal, salt and pepper in a medium bowl.
Heat 2 inches of oil in either a heavy skillet to 350°F (or until it sizzles immediately when you toss in a small piece of bread).
Toss the oysters in the seasoned flour, shake off the excess.
Fry oysters in a couple of batches until golden and very crispy, usually about 3 to 5 minutes, depending on the size of the oysters. Drain on paper towels.
In a small bowl, mix together the mayo, sriracha, and lemon juice. Keep in the fridge until ready to use.
Butter both sides of bread slices. Heat a non-stick skillet over medium heat. Add the bread and toast until golden on both sides (you'll probably need to toast the slices in batches).
To assemble the sandwich, spread the sriracha mayo onto one side of the bread slices.
Then build upward on one slice by starting with the oysters, then bacon, tomatoes (sprinkle with a little salt and pepper), and lettuce. Top with bread slice (mayo side down). Slice and serve at once!