Heat the oil in a large pan until hot. Add the onion and cook until softened, about 1-2 minutes.
Add the beef mince to the pan and season with salt and pepper. Cook until the beef is browned and no longer pink. Drain any excess fat, if necessary.
Add the taco seasoning, garlic powder, rice, beef stock, chopped tomatoes, sweetcorn, black beans, and green chillies to the pan and stir to combine. Bring to a boil, cover, and reduce the heat to medium-low.
Cook for 18-20 minutes, until the rice is soft. Turn off the heat, top with the grated cheese, and place the cover back on until the cheese is melted.
Serve immediately with your favourite toppings, such as sour cream, avocado, coriander, tomatoes, jalapeños, and black olives.