Dice the chicken breast.
Cut the onion, carrot, celery, and tomato into bite-sized pieces.
Heat olive oil in a pot and sauté the chicken breast.
When the chicken breast is partially cooked, add the vegetables and stir-fry together.
Once the vegetables are softened, pour in water and tomato sauce.
Season with salt and pepper.
Simmer over medium heat for about 20 minutes.