Cut 2 limes into wedges; reserve. Cut remaining limes in half. Squeeze juice from 1 halved lime over tomatillo; sprinkle with 1/4 teaspoon of the sea salt, and stir. Let stand 20 minutes. Stir tomato, onion, and chile into chopped tomatillo; sprinkle with black pepper and 1/2 teaspoon of the sea salt. Sprinkle fish with 1 teaspoon of the salt. Cook fish in 2 teaspoons hot canola oil over medium-high until golden brown, about 2 minutes on each side.
Stir together mayonnaise, juice of remaining 1 halved lime, and 1/2 teaspoon of the sea salt; set aside. Stir together tempura batter mix and seltzer water; coat sea beans in batter. Heat remaining canola oil to 350°F in a Dutch oven over medium-high. Fry beans until crispy, about 2 minutes.
Divide fish evenly among tortillas. Top with tomatillo mixture, shredded cabbage, and desired amount of mayonnaise-lime sauce. Sprinkle with cilantro leaves; serve with sea beans and reserved lime wedges.
Bracero Cocina de Raíz, San Diego, CA