Fry the leek, Chinese cabbage and bell peppers with 1 tablespoon of rapeseed oil in a non-stick pan for 8 minutes, then pour off the liquid that has formed.
At the same time fry the sausages in a second pan in 1 tablespoon of rapeseed oil until light brown (!).
Put the hollandaise in a small bowl. Mix in the sambal oelek, garlic and thyme and do not season with salt or vegetable stock.
Put half of the vegetable mixture in a baking dish, sprinkle with 1/3 of the gratin cheese. Pour half of the hollandaise over it, pour in the rest of the vegetables, sprinkle 1/3 of the gratin cheese again and pour the rest of the hollandaise over it. Place the sausages on top and sprinkle with the remaining cheese.