Drain and rinse black beans; set aside to dry slightly. Chop lettuce, avocado, pepper, tomatoes, and green onions. Cook or defrost corn. Grate cheese, if needed, and set out tortilla chips.
To make the dressing, add all ingredients to a blender or food processor. Blend on high speed until the oil and lime juice are emulsified into a smooth mixture. The cilantro, garlic, and jalapeño should be very finely diced. Transfer to a jar or small dish.
Assemble salads as desired. (You can pile everything together into a big bowl, drizzle with 2-3 tablespoons of dressing, toss well, and serve. If feeding a crowd, though, I prefer to set out all the fixings assembly-line style and let people build their own bowl for customized salads. The dressing and chips are really key, so encourage everyone to toss salads very well to distribute those ingredents well throughout, and set extra dressing and chips on the table!)
Notes
Corn: If using fresh corn, just grill or boil it then slice off the cob. If using canned corn, simply drain and use as-is. If using frozen corn, you can steam or just let it defrost on the counter for an hour or so. This is actually my favorite lazy way to do it. And if you purchase fire-roasted frozen corn kernels, you still get great flavor and those beautiful black char marks with zero effort.
Dressing: Extra dressing will keep well tightly covered in the fridge for up to 1 week. Give it a good shake and add a quick squeeze of fresh lime juice right before using again. It also works well as a marinade for chicken or shrimp—just add a little water to thin it out a bit if you need more for this purpose.
Leftovers: If you have extra ingredients, store beans and veggies together in an airtight container in the fridge. Store chips and dressing separately. Assemble as desired; it should stay good for 1-2 days.