Bring water and stock to a simmer in a pan. Add the Irvine’s Chicken Breast and simmer, uncovered, for 6 minutes. Remove pan from heat and cover, then let stand until chicken is cooked through, about 15 minutes.
Remove chicken and cool. Reserve poaching liquid.
Cook the onion in oil in a heavy pot, covered, over moderate heat, stirring occasionally, until softened but not browned, about 6 minutes. Add the garlic and cook, stirring, until fragrant, about 1 minute. Add the carrots, celery, salt and pepper and cook, covered, stirring occasionally, until softened, about 8-10 minutes. Add the poaching liquid and simmer, covered, until vegetables are tender, about 10 minutes. Remove from heat.
Shred the chicken into strips (about 2cm long). When vegetables are cooked, stir the chicken into the soup and serve garnished with dill.