Thinly slice the chicken breasts and season with salt and pepper.
In a small bowl, whisk together the chicken stock, soy sauce, and vinegar.
In a large wok, drizzle oil over high heat. When thoroughly heated, add the sliced chicken breasts. Cook, stirring often, until golden on all sides. Toss in the garlic and onions, then the chicken stock mixture.
Once the onions begin to soften, stir in the tomatoes, cilantro, aji amarillo, and additional salt and pepper to taste.
Remove from heat and serve immediately with French fries and rice.