In a medium bowl, combine the cabbage with 1 tablespoon of lime juice and a generous pinch of salt and pepper. Using your hands, squeeze and massage the cabbage until just wilted. Light a grill and oil the grates. Brush the scallions and fish with oil and season with salt and pepper to taste. Grill over high heat, turning once, until the scallions are charred and the fish is cooked through, about 6 minutes.
Chop the scallions and add them to a medium bowl along with the avocado, chopped cilantro, and the remaining 2 tablespoons of lime juice and stir to combine. Season with salt.
Serve the fish, cabbage, and guac in the warm tortillas, garnished with the jalapenos, radishes, sour cream, and cilantro leaves.
"The Portlandia Cookbook: Cook Like a Local" by Fred Armisen, Carrie Brownstein and Jonathan Krisel © Clarkson Potter 2014. Reprinted with permission from Clarkson Potter. All rights reserved.