In Kenya boda boda is more common i think. I cant remember anyone saying pikipiki. Even tho its not exactly rendering to the same thing. In Kenya english words are also widely used. Idk abiut Tanzania as ive never been there.
Vitunguu is both singular and plural and therefore stands for both "onion" & "onions". Consequently, "green peppers and onion" is correct and should be accepted as such.