Onions are pretty fundamental to Western cooking as well, but they're not a staple in the sense that people will starve if they're unavailable, the way potatoes or wheat are.
I've always thought staples were the bulk of the energy content in cultures, i.e. rice, bread from wheat/corn/etc, potatoes. I checked anyway, there's a bunch more I hadn't considered!
Yes, but when you get your vitamins from one main vegetable, it can be a public health problem if a moth eats the whole crop several years in a row. NIGERIA has been limping along since 2016.
https://en.wikipedia.org/wiki/Staple_food