Make the creamy green sauce by combining all the ingredients in a mini food processor or blender and processing until smooth. To thin the consistency, add water about 1 teaspoon at a time. Taste and add more lime juice and salt as needed.
Make the slaw by whisking together the mayonnaise, yogurt, sriracha, honey, and salt in a mixing bowl. Add the cabbage and red onion and toss until evenly coated.
Cut the cod fish into 2- to 3-inch fingers.
Set up your fish breading station: In one shallow bowl, whisk together the flour, chili powder, ¼ teaspoon salt, and a few grinds of black pepper. In another whisk together the egg and 1 tablespoon water until smooth. In a third bowl, stir together the panko breadcrumbs and remaining ¼ teaspoon salt.
Working a few at a time, prepare the fish: dredge each piece in the flour, dip in the egg, and then roll through the panko until coated all over. Arrange the breaded fish in a single later on a baking sheet or plate.
Set a heavy skillet over medium heat, and add enough oil to make about ⅛-inch depth, for shallow-frying.
Once the oil is hot, add as many fish pieces as will fit in a single layer without crowding. Cook them until golden-brown all over and the fish is firm and cooked through, 2 to 3 minutes per side, adjusting the heat as necessary to prevent burning. Move the cooked fish to a paper towel-lined plate or sheet pan, and repeat to cook the remaining fish, adding more oil to the pan as needed.
To serve, scoop a little pile of slaw into a tortilla. Top with 1 or 2 fish pieces and a dollop of the creamy green sauce, as well as any additional condiments you like.
To bake or air-fry the fish, arrange the breaded pieces on a parchment lined baking sheet, and spray evenly with olive oil cooking spray. Bake at 400ºF or air-fry at 385ºF for 8 to 10 minutes, until lightly browned and firmed up, flipping the pieces over halfway.
Salmon, swordfish, snapper, and any other firm-fleshed fish will work in this recipe.