Add the shredded cabbage, chopped cilantro, & sliced onion to a large bowl. Toss to combine well & set aside. In a small bowl, combine remaining listed ingredients – sour cream, buttermilk, mayonnaise, garlic, lime juice, & cumin. Season with S&P as desired. Mix to combine well. Toss enough ranch dressing into slaw to coat the veggies well & reserve the rest for serving. Set aside.
Pour the oil into a medium skillet. The amount of oil needed depends on the size of your skillet & the thickness of the fish – use just enough such that the oil comes halfway up the sides of your thickest piece of fish. Preheat over medium-high heat. The oil is ready once it sizzles when you sprinkle a breadcrumb or two into the skillet.
Cut the flounder into uniform pieces that will fit inside your tortillas well, approximately 4-5 inches wide. Using paper towel, pat the fish as dry as possible, then give each piece a liberal dusting of the taco seasoning.
Place the rice flour, beaten eggs, & panko breadcrumbs in separate shallow bowls or containers. Season each bowl with S&P. Working one by one, give each portion of fish a light dusting of flour, followed by a light coating of egg. Place the fish into the panko breadcrumbs, pressing to adhere & coat the fish as completely as possible. Shake off any excess breading & set aside. Repeat with the remaining fish.
Once the oil is hot, use tongs to carefully transfer the prepared flounder into the skillet. Work in batches. Cook 1-2 minutes per side, or until golden brown & cooked to your liking – total cook time depends on the thickness of the fish. Once both sides are golden brown, transfer the fried fish to a paper towel-lined plate to drain excess oil. Season with a good pinch of salt while the fish is still warm. Repeat.