Line a heavy skillet with aluminum foil and spray with vegetable spray. Set aside.
Remove the husk from the tomatillos and rinse them. Slice the tomatillos crosswise. Set aside.
slice the jalapeño in half, vertically and remove the seeds and white membrane.
Heat the skillet over medium high heat and place the tomatillos, jalapeños and the unpeeled clove of garlic in the pan. Cook the vegetables for about 5-6 minutes or until they start to blister and become fragrant. Use a pair of tongs and flip the vegetables over. Continue to cook for 2-3 more minutes and remove from heat.
Remove the skin from the blistered garlic and discard. Transfer the tomatillos, jalapeño and garlic to the bowl of a food processor. Pulse several times until fairly smooth.
Peel and seed the avocado and place it in the bowl of the food processor. Add the lime zest, juice, cilantro and salt. Pulse until the salsa is smooth and creamy.
You can serve this immediately, or if you're saving it for later, transfer the dip to a airtight container. Place a piece of plastic wrap over the container and lightly press the plastic into the surface of the salsa. This will prevent it from discoloring over the course of a few hours. Can be made 4-5 hours ahead of serving.
Serve salsa with tortilla chips and a good margarita or cerveza.