Halve or quarter the fish fillets so they will fit into a medium-sized saucepan. Combine the chicken broth, jalapeno juice and lime juice. Bring to a boil, then reduce heat to medium-low. Add the fish pieces and simmer 3 to 4 minutes.
Remove the pan from the heat and let the fish cool in the liquid for 30 minutes.
Remove the fish and pat dry with paper towels. Place the fish in a medium-size bowl and break into large flakes with your fingers or a fork. Add the scallions, tomato and avocado cubes then toss gently to mix. Season with the salt and pepper. Arrange 2 tablespoons of the fish filling down the center of each tortilla. Divide the lettuce among the tortillas and top each taco with 1 tablespoon tomatillo salsa.
See Tomatillo Salsa Recipe