Combine garlic, cilantro, mayonnaise, buttermilk, sour cream, and lemon juice in a mini processor. Add a pinch of salt and process until smooth. Taste and add more salt if necessary. (An immersion blender would work for this, too!)
Line a half sheet tray (18 x 13 inches) with aluminum foil and turn on your broiler (or heat oven to 500° F).
Follow thirschfeld's advice and open your chips over the lined tray from the bottom of the bag rather than the top. This keeps the small broken bits hidden on the bottom. Spread out the chips.
Sprinkle about half of the cheese over the chips, then sprinkle with black beans, little blobs of refried beans, and the onions. Cover with the rest of the cheese.
Broil the chips until all of the cheese has melted, 4 to 5 minutes . (This step might take a few more minutes if you're baking them.)
While you're broiling the chips, add the lettuce, tomatoes, olives, and avocado to a medium bowl. Toss with about 2/3 of the dressing, then add more dressing if desired and toss again.
Once the chips are done, remove from the oven and scatter the dressed salad over the top of them. Serve with hot sauce. And plenty of napkins.