Set up your grill for even medium-high heat. If using a charcoal grill, distribute the coals evenly. If using a gas grill, heat both sides evenly.
Place the whole tomatillos, scallions and jalapenos on a cooling rack in a single layer. Drizzle with olive oil and sprinkle with salt. Place the cooling rack on the grill and cook, pulling the cooling rack off the grill to flip the vegetables, until softened and charred on both sides, about 5 minutes per side. Using a knife, scrape off the skin from the jalapenos. If you want the salsa to be spicy, leave in the seeds. If you do not, remove the seeds and ribs from the jalapenos.
To a blender or a food processor, add the tomatillos, scallions, jalapenos, cilantro, cumin, garlic, lime juice and olive oil. Blend until a salsa forms. Blend as much as you need to reach the consistency of the salsa you like. Add salt to taste. The sauce will keep in the refrigerator for up to 1 week.