It's sweet banana, not plantain. "Kebab" is also a popular (if less weird) topping option.
Incidentally, a lot of the pizza places here do really quite terrible quality pizza - I think because the pizza is more the pretext for selling alcohol (liquor laws are quite strict).
Cavendish Banana : https://en.m.wikipedia.org/wiki/Cavendish_banana
Or Plantains a.k.a. (Cooking Banana) : https://en.m.wikipedia.org/wiki/Cooking_banana
Pineapple : https://en.m.wikipedia.org/wiki/Pineapple
EDIT: Add; Pineapple and Cavendish banana