Marinating tender sea bass in turmeric, lal masala, and ketchup before coating with green chutney keeps each layer of flavor distinct and adds a beautiful ring of vibrant color to this crispy fried fish, traditional to Parsi cuisine.
Toss together fish and turmeric in a large bowl until evenly coated. Add lal masala, and toss to coat. Add ketchup, and toss until fish is evenly coated. Cover and chill 30 minutes.
Slather fish with green chutney until coated in a thick layer. Place panko and beaten eggs in separate shallow bowls. Pour oil to a depth of 1/4 inch in a large skillet; heat over medium-high to 350°F. Working with 1 piece of fish at a time, dredge in panko, and lightly dip in beaten egg. Without shaking off excess egg, place fish in hot oil. Repeat dredging and dipping process with half of fish pieces, arranging in a single layer in skillet.
Cook fish, turning every 2 minutes, until golden brown, crisp, and cooked through, 8 to 12 minutes. Transfer fish to a baking sheet lined with paper towels. Repeat with remaining fish, panko, and egg. Garnish fish with sliced red onion and lemon slices; serve immediately.
Find lal masala at South Asian markets or online.