Peel the onions, clean and wash the leek. Cut both into rings.
Heat 2 tablespoons of oil in a pan. Add onions and leek and sweat. Add tomato paste and sweat with it, it can get some color. Caramelize with the honey or agave syrup. Pour in the vinegar and the vegetable stock and bring to the boil. Let the leek and onion sauce simmer for about 10 minutes. Finally, season with salt, pepper and oregano.
At the same time, heat 1 tablespoon of oil in a second pan and fry the sausages.
Arrange the sausages with the leek and onion sauce and serve.