Bowl 1: Mix flour, salt, and pepper.
Bowl 2: Whisk together milk and apple cider vinegar; let sit for 5 minutes.
Bowl 3: Stir together cornmeal, breadcrumbs, parsley, and Cajun seasoning.
Dredge each tomato slice in the flour mixture, dip into the milk mixture, then press into the cornmeal and breadcrumb mixture to coat.
In a large skillet over medium-high heat, add oil. When hot, place coated tomato slices in the skillet without overlapping. Fry 3 minutes per side, until golden brown. Transfer to a plate lined with paper towels to absorb any excess oil. Serve hot.