Preheat oven to 400F.
Slice the top 1/4-inch off the stem end of the garlic head, exposing the cloves. Place the garlic onto a square of aluminum foil and drizzle with about 1 tablespoon EVOO. Wrap the foil up around the garlic to enclose it and roast it in the oven until golden brown and very tender, about 40 minutes.
While the garlic is roasting, place the chicken into a medium pot with the bay leaves and onion. Fill the pot with water and bring up to a simmer. Place the chicken into the pot and simmer until cooked through, about 10 minutes. Remove the cooked chicken from the broth, dice into bite-sized pieces and reserve. Strain the cooking liquid, reserving 4 cups worth.
Place a large pot over medium-high heat with 2 turns of the pan of EVOO, about 2 tablespoons. Add the carrots and leeks to the pan, and cook until tender, about 5 minutes.
While the veggies are cooking, squeeze the cloves from the head of roasted garlic into a small bowl. Add a splash of stock to the cloves and mash into a paste. To the pot with the carrots and leeks, add the lemon zest, mashed garlic, remaining chicken stock and reserved poaching liquid and bring up to a bubble.
Add the cabbage and egg noodles to the pot, and cook until both are tender, 3-4 minutes. During the last minute of cooking, add the reserved chopped chicken to the pot. Season the soup with salt and pepper and stir in the lemon juice and herbs.