Clean the fennel, cut in half, cut out the stalk and cut the fennel halves into very thin slices. Cut the onion into fine strips. Peel the sweet potatoes and cut into approx. 1 cm cubes. Halve the date tomatoes and quarter the mushrooms.
Heat the olive oil in a large pan and fry the potatoes in it. Add the fennel, onions and mushrooms and fry briefly until the vegetables are still firm to the bite.
Place the fennel and potato vegetables with the halved date tomatoes in an ovenproof dish, season with salt and pepper, pour in the vegetable bouillon and place in the oven preheated to 160 degrees. Halve the cod, season with salt and pepper to taste and place on top of the vegetables after 10 minutes. Cook for another 10 minutes depending on the thickness of the cod.
Take the pan out of the oven and garnish the fish with fennel greens.