Combine flour, 1 teaspoon salt, and 1 teaspoon pepper in a shallow bowl. Pour buttermilk in 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 the flour mixture to coat, dip into the buttermilk, and finish by pressing each side of the tomato into the cornmeal mixture to coat. Lay coated tomato slices onto a baking sheet; rest to let tomatoes absorb flavor of 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 the hot oil and cook until golden brown and floating, 2 to 3 minutes. Drain on a plate lined with paper towel.
Whisk ranch dressing, cajun seasoning, and hot pepper sauce together in a small bowl; serve with the fried tomato slices.
