To make the curry sauce, heat oil in a pot over medium heat. Sauté garlic and onion until fragrant, about 2 - 3 minutes. Add the chopped carrots and potatoes, stirring to combine then add water to cover. Bring to a boil then simmer for about 5 minutes or until the vegetables are just cooked. Add the Japanese curry cubes and mix until the sauce has thickened. Loosen with a little water if needed.
To make the chicken katsu, pat dry then pound with a meat hammer to tenderise and make thin. Season both sides with garlic powder, salt and pepper. Dip the chicken pieces into flour, the beaten eggs then into the panko breadcrumbs, pressing firmly to stick. Heat oil in a pan until shimmering then cook the chicken on both sides for about 5 minutes until crisp and golden brown. Slice the katsu into strips and serve with steamed rice and a generous amount of the curry sauce.
