Cut tomatoes into ½-inch thick rounds. Sprinkle both sides with a pinch of kosher salt and black pepper. Set aside.
Set up the dredging station. – Bowl 1: Combine flour, salt, and black pepper.
– Bowl 2: Whisk together milk and apple cider vinegar. Let sit for 5 minutes.
– Bowl 3: Stir together cornmeal, Panko breadcrumbs, parsley, and Cajun seasoning.
Working one at a time, dredge tomato slices in the flour mixture, dip into the milk mixture, then press into the breadcrumb mixture to fully coat.
Set a large skillet over medium-high heat and add enough vegetable oil to cover the bottom. When hot, add the coated tomato slices in a single layer without overlapping. Fry for 3 minutes per side, or until golden brown.
Transfer to a paper towel–lined plate to drain excess oil. Serve hot.