Add 1 tablespoon of water to the cornstarch and stir to make a slurry. Stir together the lemon juice and zest, honey, chicken stock, and cornstarch slurry in a bowl or jug. Set aside.
Heat the olive oil in a large ovenproof casserole dish over medium heat. Add the chicken and brown well on both sides. This should take about 10 minutes. Remove from the pan and set aside onto a plate.
Preheat the oven to 400 F.
Add the onion, carrot, and celery to the pan. Cook for 5 minutes until softened, then add the garlic and cook for about 2 minutes, stirring constantly.
Add the potatoes and lemon chicken stock mixture to the pan. Season with salt and pepper to taste. Bring to a boil and stir for about 3 minutes, until thickened. Add the chicken back to the dish.
Place the lid on the casserole dish and bake in the oven for 35 minutes.