Heat neutral oil in a shallow, heavy-bottom fry pan to 360 degrees F.
Season both sides of the tomato slices with salt and set them aside on a paper towel lined plate to absorb some of the moisture.
Place 1/2 cup flour in a shallow baking dish. In a separate, baking dish, whisk together the cornstarch, baking powder, baking soda, a pinch of salt, a few turns of black pepper, and remaining 1/2 cup flour. Then add the egg and the buttermilk and whisk to combine. In a third baking dish, combine the breadcrumbs with a pinch of salt and a few turns of pepper.
Coat the tomato slices first in the plain flour. Then dip them in the batter, allowing any excess batter to drip off. Finally, coat them in the breadcrumbs. Fry the battered and breaded tomatoes for 2 minutes per side, until golden brown. Use a spatula or slotted spoon to transfer them to a cooling rack set over a baking sheet. Season them with salt and reserve.
Fry bacon on a griddle until crisp and to desired doneness. Remove from the griddle onto a cooling rack set over a baking sheet. In the same griddle with the bacon fat, toast bread, flipping it over a few times to evenly distribute the bacon fat. Toast until crispy and golden brown.
To make the schmear, combine mayo, herbs, salt, pepper, and lemon juice and whisk to combine. (This can be done in advance).
Spread 1 tablespoon of mayo on each slice of bread. Top each side with 3 slices bacon, 2 slices tomato, 2 lettuce leaves, and other slice of bread. Slice in half and enjoy right away or wrap up for later. If wrapping, make sure the sandwich is cool before wrapping it up so it doesn’t get soggy.