1Mix 1/3 cup of water with the fish sauce in a small bowl and set aside. Combine shallots, garlic, black pepper, and red pepper flakes in a separate bowl and set aside.
2Heat 1/3 cup of water and 1/3 cup of sugar in a large skillet over medium heat, stirring occasionally until sugar turns deep golden brown. Gently stir in the fish sauce mixture and bring to a boil. Stir in the shallot mixture and cook until shallots soften, then add the catfish. Cover and cook the catfish until the fish flakes easily with a fork, about 5 minutes on each side. Place catfish on a large plate, cover, and set aside. Increase heat to high and stir in 1/2 teaspoon of sugar. Stir in the lime juice and any sauce that has collected on the plate. Bring to a boil and simmer until the sauce has reduced. Pour sauce over the catfish and garnish with green onions and cilantro.