Prepare the dressing: mash the avocado and lemon juice with a fork until fairly smooth.
Add remaining dressing ingredients and whisk with a wire whip until smooth.
Chill until needed.
Preheat oven to 400°F.
Place taco shell boats upside down in a baking sheet and bake for 5 minutes; turn right side up and bake another two minutes; allow to cool and crisp a little as they cool.
Warm barbacoa and shred the meat with a couple forks or use your fingers, discarding extra liquid. You can use your own recipe for barbacoa or machaca if you like; my back was hurting so I lazied out with some pre-prep. Every cook needs a day off now and then!
For each taco boat, add one cup lettuce, 1/4 cup barbacoa, 1/4 of an egg, 1 tablespoon of cheese, 2 sliced cherry tomatoes, and a few sliced black olives.