I don't know why avocados on toast is a meme used to insult millennials.
When you go to the grocery store in the USA and you look at the avocado section you are probably buying a
Hass Avocado. Hass avocados are grown in California, which is part of the USA, so they don't have to go through customs or some other dumb process to get here. Hass trees produce year-round, it's not particularly difficult to grow.
Avocados are high in healthy fats, low in carbs, and they have a few other vitamins in them. They also taste good. You should try a sandwich on a toasted roll//bun with avocado, tomato, a fried egg, and cheese. Add spicy mustard for bonus points.
They aren't even that expensive. A $ per avocado isn't a lot when you consider the nutritional quality and weight of the edible portion. And usually you can get them for cheaper than that.