PREP: Preheat the oven to 450 F / 230 C. Pour the avocado oil onto a rimmed baking sheet. When the oven comes up to temperature, place the oiled baking sheet into the oven until the oil is shimmering hot (although not smoking), about 5 – 6 minutes.
LAYER: Trim the roots from the green onions. Slice the top of the head of garlic off and discard. Cut the onion in half through the root, then peel and discard the skin. When the oiled baking sheet is hot as described above, use tongs to place the onion on the sheet, cut sides down. Add the head of garlic, cut side up, as well as the green onions. Spread the green onions out so they’re as close to a single layer as you can manage. Be careful, as the hot oil may splatter a little when the vegetables are added and make sure none of the green onion tips overlap the edge of the baking sheet, or they will burn.
ROAST: Roast the green onions, turning every five minutes or so, until they are tender and soft, with golden charred marks throughout. For larger, thicker, wild or farmer’s market green onions, this will take 15 – 20 minutes. For thinner, smaller or grocery store green onions, this will take much less time, so you’ll want to watch them at around the 10 – 12 minute mark. You’ll need to keep an eye on them, because you want lovely golden brown char marks, but you don’t want the green onions to burn or blacken as that will result in a bitter salsa. When the green onions are done, remove them from the baking sheet and continue to roast the onion and garlic until the onion halves are a deep golden brown, about 20 – 25 minutes total cook time.
COOL: Set the garlic aside to cool slightly. Remove the root ends of the onion and roughly chop the onion into a few chunks. Add the green onions (both white and green parts) and onion to a high powered blender, along with the chicken broth, cilantro, lime juice and sea salt. When the garlic is cool enough to handle, squeeze the roasted garlic from the cloves and add it to the blender, too. Puree on high until the salsa is evenly combined and smooth. Taste and add additional lime juice or salt if you like. For a thinner salsa, just add an extra splash or so of broth or water.
STORE: Keep in an airtight container in the fridge for 2 – 3 days or the freezer for a few months. The salsa will separate a little after some time in the fridge, but a quick stir will set things right again.