Heat a large pot over medium-low heat and add the olive oil and butter. Once melted, add in the onion, carrots, celery, garlic, ginger, salt and pepper. Stir and cook until the vegetables are slightly softened, about 5 minutes. Stir in the lemon zest and chicken. Add in the lemon slices, chicken stock, bone brother and water. Bring the mixture to a boil.