Preheat the oven to 375 degrees . Arrange the bacon on a broiler pan and bake until crisp, 15 to 18 minutes. Place the bread on a rack-lined baking sheet and toast to light golden.
Meanwhile, salt the tomatoes liberally and drain on paper towels for 10 minutes. Heat 1/4 inch oil in a large skillet. Put the flour, eggs and fine breadcrumbs on separate plates. On another plate, mix the panko, cheese, lemon zest and ground fennel (or fennel pollen); season with pepper. Coat the tomatoes in the flour, eggs, fine breadcrumbs and panko. Shallow-fry the tomatoes in the hot oil, turning once, until golden, 4 to 6 minutes.
Make the aioli:
Using a food processor, mix the egg yolk, tarragon, garlic, mustard and lemon juice; season with sea salt. Slowly stream in the grapeseed oil until the sauce is thick and emulsified.
Slather the toast with the aioli. Layer the sandwich with the bacon, lettuce and fried green tomatoes (FGTs). Cut and serve.