Make the vinaigrette: In a medium bowl or resealable container, whisk together

the buttermilk, mayonnaise, lemon juice, olive oil, garlic, oregano, and cayenne, if using. Season to taste with salt and pepper. Cover and store in the refrigerator until ready to use.

Make the tomatoes: In a shallow bowl or pie pan, whisk together 1/3 cup of the flour, the salt, and paprika. In another shallow bowl, whisk together the buttermilk and egg white. In a third shallow bowl, whisk together the remaining 1/3 cup flour and the cornmeal. Set a wire rack inside a rimmed baking sheet lined with aluminum foil (for easy cleanup). Coat each tomato slice with the flour mixture, then dip into the buttermilk, then coat with the cornmeal mixture. Arrange the breaded tomato slices on the wire rack in a single layer.

Heat the oil in a large cast-­iron skillet over medium-high heat until shimmering. You'll know the oil is ready if you sprinkle in a little flour and it sizzles immediately. Working in batches to avoid overcrowding the pan, fry the tomato slices until golden brown, 2 to 3 minutes per side. Transfer the fried tomatoes back to the wire rack and sprinkle with the flaky sea salt.

Assemble the salad: Spread the arugula on a serving platter. Arrange the fried green tomatoes on top. Sprinkle the cherry tomatoes and onion slices over the fried tomatoes and garnish with the oregano. Drizzle on the dressing and serve.