Preheat the oven to 425°F (200°C). Halve the tomatillos then place them on a rimmed baking sheet with the garlic and the 1 whole jalapeño. Drizzle with 4½ teaspoons of the olive oil, and roast, tossing once during cooking, until the tomatillos are quite soft, 20 to 25 minutes.
Squeeze the garlic cloves from their papery skins, discarding the skins. Remove and discard the jalapeño skins, stems, and seeds. Add the garlic, jalapeño, tomatillos, ½ cup of the cilantro, and the coconut cream to a food processor or blender. Squeeze in the juice of ½ lime. Pulse several times, then process until smooth.
Use a spatula to scrape the tomatillo mixture into a saucepan, then bring it to a gentle simmer over medium low heat; don’t let it boil. Cover, remove from the heat, and keep warm.
In a small bowl, combine the radishes, the 1 sliced jalapeño, the remaining cilantro leaves, the juice of the remaining ½ lime, and 1½ teaspoons of the olive oil. Toss gently to combine.
Pat dry the cod fillets with a paper towel. Season both sides of the fish with salt and pepper.
Heat a heavy, 12-inch nonstick or cast-iron skillet over high heat. When the pan is hot, add the remaining 2 tablespoons of olive oil. Carefully place the fillets in the pan, skin side down. Lower heat to medium and let sizzle until fish is golden and caramelized around edges, 2 to 3 minutes. Carefully flip fillets and cook until the other side is golden and crisp, and the fish is flaky and opaque, 2 to 3 minutes more.
Spoon about 1/4 cup of sauce onto each of the four plates, top with a fish portion, then add another 1/4 cup of sauce. Garnish each portion with a pile of the radish salad. Serve right away.