Bawang is generic for onion and garlic. Bawang merah is onion, Bawang putih is garlic
Bawang merah and Bawang putih size is like a big cherry, for big onion bawang bombay is used
While “I like onions” is not incorrect, “I like onion” is more correct. We tend to use the singular forms of fruit & vegetetables when referring to fruit & veg in general.
Just for information, it seems they also use in Indonesia "bawang bombay" in order to say onion
Bawang bombay is big onion. Size of an orange