In parts of East Africa, almost only smoked fish or meat is cooked together with groundnuts (peanuts). There is however no reason why fresh fish (or meat) cannot be used as well as is very common in West Africa, where they do a lot of mixing of ingredients, some of which would be quite astonishing to especially "conservative" East Africans. My experience, though is that their dishes are really delicious & they have more variety.

The tuna/canned fish alternative is for someone not having quick access to fresh/smoked alternatives and needs something cooked fast.

The sauce can be enriched or varied with other vegetables, like zucchini, brussels sprouts, carrots, fresh peas (cooked), etc and spices.

This makes a good accompaniment for ugali, rice, chapati, potatoes, sweet potatoes, steamed cassava, etc [see respective recipes of chapati & ugali (posho)].