Combine tomatillos, onion, garlic, chilies, water and vinegar in a saucepan. Bring to a boil and simmer for about 15 minutes. Transfer solid ingredients to a blender. Add avocado, chopped cilantro, lime juice, and 1tb of the cooking liquid. Blend just until smooth, adding additional cooking liquid if necessary. Transfer to a saucepan, season with salt and pepper and heat through just before serving. Sprinkle snapper with oregano, salt and pepper. Lightly coat grill with vegetable spray. Grill fish over medium-high heat until cooked, but not falling apart, about 4 minutes on each side. Presentation: Spoon a puddle of salsa onto 4 dinner plates and place snapper on top of sauce. Arrange line wedges on or around the fish; garnish with sprigs of cilantro and serve.