Heat a large pot over medium heat with the oil. Dice the vegetables into 2cm pieces and set aside. Add the onion and sauté for a couple of minutes, or until softened and fragrant. Stir in the beets, carrots, and potatoes, and cook for five minutes more, stirring occasionally. Add the cabbage and cook for an additional two minutes, followed by the garlic for another minute. Stir in the salt, paprika,  pepper, and cayenne pepper. Add the mustard and the balsamic vinegar, stir, and pour in the vegetable stock.

Increase the heat to high and bring the soup to a rolling boil. Add the lentils and reduce the heat to medium-low, then simmer for 40-45 minutes, or until the vegetables are softened. Stir in the dill, taste, and add seasoning as needed. Serve hot with a little yogurt and dill. The soup freezes well and will keep in the refrigerator for up to three days.