Duck tacos with tomatillo salsa

Duck breasts, skinless, frozen	2
Water	1 ½ cups
Lime juice	½ cup + 2 tablespoons
Salt, kosher
Tomatillos, husked, quartered	½ pound
Garlic, chopped	5 cloves
Serrano chiles, chopped	2
Onion, coarsely chopped	1 small
Cilantro leaves	3 tablespoons
Avocado, Haas, ½-inch dice	1
Tomato, Roma, diced	1
Tortillas, corn, warmed
Sour cream	Optional

1. Place the duck, water, and 1/2-cup juice in a pressure cooker, close and lock the lid, press Poultry (if you have it), and set the timer to 30 minutes. 
2. In a blender, combine the tomatillos, garlic, serranos, onion, cilantro, and 2-tablespoons juice; process to a coarse puree. 
3. Transfer the salsa to a bowl, and stir in the avocado and tomato; season with salt. 
4. Shred the duck with forks, and serve with the tomatillo salsa and sour cream with warm tortillas.