Combine flour, 1 teaspoon salt, and 1 teaspoon pepper in a shallow bowl. Pour buttermilk into a second shallow bowl. Mix cornmeal, parsley, paprika, 1 teaspoon salt, 1 teaspoon pepper, and cayenne pepper in a third shallow bowl.
Dredge each tomato slice in flour mixture to coat, dip into buttermilk, and finish by pressing both sides of tomato into cornmeal mixture to coat. Lay coated tomato slices on a baking sheet; set aside to let tomatoes absorb the coating, 10 to 15 minutes.
Heat oil in a deep-fryer or large saucepan to 350 degrees F (175 degrees C).
Gently drop tomato slices into hot oil and cook until golden brown and floating, 2 to 3 minutes. Drain on a plate lined with paper towels.
Whisk ranch dressing, Cajun seasoning, and hot pepper sauce together in a small bowl; serve with fried tomato slices.