In a bowl, mix the lemon juice, ginger-garlic paste, red chili powder, black pepper, turmeric, and salt.
Rub the marinade over the fish pieces until evenly coated.
Let the fish rest for 30 minutes at room temperature, or refrigerate for 1 hour for deeper flavor.
In a wide bowl or plate, mix the all-purpose flour, cornstarch, red chili powder, black pepper, garlic powder, onion powder, Italian seasoning, and salt. Set aside.
In another bowl, mix the all-purpose flour, red chili powder, and salt. Add water a little at a time until you get a smooth, medium-thick batter, similar to pancake batter.
Lightly coat each marinated fish piece in the dry flour mixture.
Dip it into the wet batter, then coat it again in the dry flour mixture. Press gently so the coating sticks well.
Heat the oil in a deep skillet, Dutch oven, or frying pan over medium heat.
Carefully add the coated fish pieces to the hot oil. Fry in batches until golden brown, crispy, and cooked through.
Do not overcrowd the pan, or the fish may turn soggy.
Remove the fried fish with a slotted spoon and drain on a paper towel-lined plate.
Serve hot with lemon wedges, tartar sauce, ranch, hot sauce, or your favorite dipping sauce.