Cut chicken breast and vegetables into bite-sized pieces.
Heat olive oil in a pan and sear the chicken breast until golden brown.
Add onion and garlic, sauté together.
Add tomatoes and other vegetables (such as bell peppers and broccoli), and stir-fry together.
Pour in tomato sauce and water, bring to a boil.
Season with salt and pepper, cover with a lid, and simmer over medium heat for 15 minutes.