1Preheat oven to 400 degrees F; line a baking sheet with aluminum foil. Arrange bacon on baking sheet and bake until crispy, about 15 minutes; cut in half and drain on paper toweling.
2Arrange flour, egg beaten with the water, and cornmeal in three shallow bowls to form an assembly line; season cornmeal generously with salt and pepper. Slice tomatoes into 1/2-inch slices and dredge tomato slices in flour, egg, and cornmeal, pressing to adhere. Set aside on waxed paper lined platter.
3Heat 1/4 inch of oil in a large skillet over moderately high heat. Cook tomatoes, in batches if necessary, until golden and crisp, turning once, about 5 minutes total; drain on paper toweling.
4On a work surface, arrange 4 pieces of toast. Spread each with mayonnaise. Layer on fried tomatoes, bacon, and arugula. Top with remaining toast and cut in half.