Since we replaced our gas stove with an Origo 3000 spiritus stove we don’t have an oven anymore. A spiritus oven exists, but we found it too expensive at the time. So we bought a simple Omnia, an oven that you put on the stove. It has tree parts: the lower part spreads the heat, the middle part contains your food and has a hole in the middle where the heat comes through. On top it has a cover.
In dutch they are called ‘wonderpot’ and were used frequently in the old days. You can still find some nice ones secondhand. Usually they have a glass cover, which I don’t want on a boat. A friend of ours made one himself. It works very well!
We use it for bread, cookies, cakes, … even tried a pizza once (I would not recommend heating a pizza from the store, unless you want to cut out a hole in the middle)