Pour the lime juice over the diced onions. Let sit for about 5 minutes.
In a separate bowl, roughly mash the avocados with a fork (leave some chunks!), then add remaining ingredients, including onions and citrus juice, and mix lightly. If needed, add more salt to taste.
Serve immediately. Enjoy! (To store, keep airtight, and sprinkle with some additional fresh lime juice on top to keep from browning.)