Wash and pat dry chicken breasts, season with salt and pepper and sear in a frying pan with 1 tablespoon of olive oil. Remove from pan and set aside. Drain the oil from pan.
Using the same frying pan add 1 tablespoon olive oil and saute celery, diced onion and carrot. Cook through allowing the flavors to meld. Return the seared chicken breasts to the pan and add the chicken stock and the white wine. Bring the liquid to a simmer and cover. Simmer until the chicken breasts are cooked through, about 20 minutes. Remove the lid and reduce the liquid until it is not so brothy. Season with salt and pepper.
While the chicken is cooking, toast the English muffins and set aside. Toast the pine nuts in 1 tablespoon of olive oil and season with salt.
Saute the remaining sliced onion, squash and zucchini, allowing for some browning. Stir gently while seasoning with salt, pepper and oregano. Continue cooking until squash is slightly browned and the onion is translucent.
Remove the chicken breasts from the pan and place on the individual dinner plates. Take the toasted English muffins and soak up some of the pan juices. Using the chicken breast as a "lean to", place it so it faces the front of the plate. Add the sauteed zucchini mixture to the plate and cover the breast and the muffin with the vegetable mirepoix. Garnish with toasted pine nuts.