For the lobster: Combine 1 cup of water with the butter, garlic and saffron in a medium saucepan over medium heat and bring to a boil. Reduce the heat to a simmer, add the lobster and simmer for 5 minutes. Remove from the heat. Drain the lobster from the cooking liquid.
Meanwhile, make the salsa: Pulse the tomatillos, avocado, cilantro, onions, garlic powder, salt, pepper and 2 cups water in a blender or food processor. Transfer to a bowl.
For the tortillas: Heat the oil in a large skillet or griddle over medium-low heat. Warm each tortilla in the skillet until pliable.
Fill the warm tortillas with the lobster. Drizzle with the salsa then sprinkle with the cheese, onions and cilantro and serve right away.