Place the water and cornstarch in a small bowl and stir well to combine. Stir in the ketchup, honey, soy sauce, chili garlic sauce (if using), and garlic.
Reserve the sauce.
Place the canola oil in a large nonstick skillet over high heat. Add half of the chicken to the pan and season generously with salt and pepper (about 1/2 teaspoon of each) and cook, stirring now and then, until browned all over, about 5 minutes. Transfer the chicken to a plate and repeat the process, adding another tablespoon or so of oil to the pan if necessary, with the rest of the chicken.
Return the first batch of chicken to the skillet along with the reserved sauce. Bring the mixture to a boil, then turn the heat to low and simmer, stirring now and then, until the sauce is thick and coats the chicken, about 5 minutes. Serve immediately.