In a large pot, heat 3 ½ liters of water until boiling. While the water heats, peel and chop the sweet potato, red potato, zucchini, and cauliflower. Keep the chopped vegetables in a bowl of cold water to prevent browning.

Once the water reaches a boil, add the bay leaves, lentils, 1 whole white onion, and the chopped sweet potatoes and red potatoes. Stir in the dill, oregano, and thyme. Add the cauliflower and zucchini to the pot. Lower the heat to medium-low to maintain a gentle simmer.

Heat the sunflower oil in a nonstick pan over medium heat. Add the grated carrots and sauté for 5–7 minutes until softened. Transfer the carrots to the pot, then add the frozen green beans, peas, and asparagus. Season the soup with 2 teaspoons of salt and 1 teaspoon of black pepper.

Chop the chicken breasts, ½ onion, and bread (if using) into large pieces. Soak the bread in ½ cup water or milk until soft, then mash. Combine the chicken, onion, soaked bread, and egg in a food processor or meat grinder. Process until the mixture is smooth and well-combined. Season with 1 teaspoon of salt and ½ teaspoon of black pepper.

Wet your hands to prevent sticking, then shape the mixture into golf ball-sized meatballs. Carefully drop the meatballs into the simmering soup. Remove the whole onion from the pot to create more space. Continue adding meatballs until all the mixture is used.

Allow the soup to simmer for an additional 10 minutes after adding the meatballs. Taste the broth and adjust the seasoning with additional salt or pepper if needed. Remove the bay leaves before serving.

Ladle the soup into bowls and serve hot. Garnish with fresh dill and, if desired, a dollop of sour cream for added richness.