Combine the Onion, chile, cilantro, and salt in a large bowl. Add the tomatillos, a few at a time, mashing and blending with a fork to a fine paste. Add the avocado; mash until thick and chunky. Adjust the seasoning. Serve with sliced tomato and chips. How To Roast Tomatillos Grill tomatillos over medium-high heat, turning occasionally, until charred and softened.