Only dice up the portion of your avocado that you’re going to use on the salad. The less exposure the avocado has to the air, then the less browning you'll see. That said, you're still going to end up with an open avocado face. A little avocado hack I’ve learned is to submerge the cut avocado completely in water. You can do this in a container and snap the lid closed until you’re ready to use the rest of it. You'll take out a perfectly green avocado! And don’t worry about the texture. Avocados are dense enough that they won’t soak up any of the water you’ve submerged it in!