In a small bowl, mix together the garlic, ginger, gochugaru, sugar, soy sauce, and sesame oil. You want a paste-like consistency.

Slice the radish into 2" x 1" x 1/2" thick sections. Cut the radish crosswise into 2-inch sections, then cut those sections in half, and slice into 1/2-inch thick sections.

In medium-sized saucepan or braiser, layer the bottom with the radish and onions. Next, spread the red pepper seasoning over the radish. Then place the fish on top of everything. Pour in about 1 to 1 1/2 cups of water. It does not need to cover the fish. Over high heat, bring to a boil. Cover, lower heat to medium-low and let simmer for about 30 minutes. About halfway through, carefully flip the fish over with a pair of tongs. And spoon the brothy sauce over the fish.

After the fish has cooked through, remove the lid, raise the heat to medium-high to bring the mixture to a high simmer. Throw in the green onions and cook for another 10-15 minutes to reduce the liquid. Periodically spoon the sauce over the fish.

Serve family-style.