Wash and cut your potatoes, carrots, and onion. Peel the carrots and potatoes. Cut the potatoes into a large dice (around ½ inch cubes), your carrots into thin rounds, and the onion into a small dice.
In a large pot over medium high heat, add 1 tbsp of oil and add the onions. Season lightly with salt and allow them to cook for 1-2 minutes then add in the curry powder and stir, add the remaining oil as needed.
Make room in the bottom of your pot and add the chicken and garlic, use more of the remaining oil as needed. Allow the chicken to cook for around 3 minutes on each side to develop color.
Add 1 cup of water to the pot and reduce the heat to medium. Allow the chicken to cook in the water for around 10 minutes to finish the cooking process. Flip half way through.
Remove the chicken from the pot and set aside. Add in the carrots and potatoes with an extra 1¼ cups of water, cover the pot and cook for 10-15 minutes or until the carrots and potatoes have softened.
While the curry is stewing, cut the chicken into bite size pieces. If you find that the chicken isn't cooked all of the way through, that's okay, we are going to be adding it back to the pot.
In a bowl, mix together the cornstarch and cold water to form a slurry. Once the carrots and potatoes have softened, slowly drizzle in the cornstarch slurry to the mix while constantly stirring. This will thicken the sauce.
Add the chopped chicken back to the pot and stir in the soy sauce. Season with salt and pepper to taste.