Heat broiler on high, positioning a rack at the highest or second highest setting under the heat.
Cover a baking sheet with foil or parchment paper and place tomatillos, jalapeno, and sliced onion on it.
Broil 5 minutes, until charred on one side. Turn tomatillos, onion and jalapeno over and broil 2 to 5 minutes longer, until charred. Keep and eye on the onion and jalapeno, they may be charred before the tomatillos are ready, so you many need to remove them and keep roasting the tomatillos. You know the tomatillos are done when they are starting to char and have turned from a vibrant green to an off greenish yellow.
Carefully transfer everything to a blender, tipping in any juice that may have accumulated. Add cilantro, salt, garlic powder lime zest, lime juice, and ¼ cup water to blender and blend to a coarse purée.
Transfer to a bowl, add more water if you would like a thinner salsa. Taste and add more salt if needed. Allow to rest in the refrigerator for 20 -30 minutes to let flavors meld and salsa to cool.
Notes
Tips and Tricks
Store salsa in an air tight container in the refrigerator for up to 4 days.