Preheat the grill to medium-high heat.

Cut the fish into 1-inch strips.

Season the fish with salt and pepper.

Sprinkle the fish with lime juice.

Grease the grill with oil to prevent sticking.

Place the fish on the grill and cook for 3 minutes on each side.

Turn the fish carefully with tongs.

Warm the flour tortillas on the cooler edges of the grill.

Transfer the warmed tortillas to a plate lined with a kitchen towel.

Fold the edges of the towel over the tortillas to keep them warm.

To assemble the fajitas, divide the fish among the tortillas.

Top the fish with salsa verde and avocado slices.

Squeeze lime juice over the avocado.

Roll up the tortillas and serve.

Remove papery husks from tomatillos and rinse well.

Cut tomatillos in half and place cut side down on a foil-lined baking sheet.

Broil for 5 to 7 minutes to lightly blacken the skin.

Place tomatillos, lime juice, onions, cilantro, jalapeno peppers, and sugar in a food processor.

Pulse until all ingredients are finely chopped and mixed.

Season the salsa to taste with salt and pepper.

Refrigerate until ready to use.

Serve the salsa with chips or as an accompaniment to Mexican dishes.