Cut the beef sirloin into bite-sized pieces. Dice the onion, potato, and carrot.
Heat cooking oil in a pan and stir-fry the beef sirloin.
When the beef is about half cooked, add the onion, potato, and carrot, and stir-fry together.
Once the ingredients are cooked through, pour in water and bring to a boil.
When the vegetables become tender, add curry powder and stir well to dissolve, simmering as you go.
Reduce over medium-low heat until thickened, then transfer to a serving dish.
Serve with rice if desired.