Stir the rice and 120ml water together in a microwave-safe bowl. Cover and cook in the microwave on High for 6 minutes until the water is fully absorbed; set aside.
While the rice is cooking, heat a large frying pan over medium-high heat and stir in the minced beef. Cook and stir until the beef is crumbly, evenly browned and no longer pink. Drain and discard any excess fat.
Reduce heat to medium and stir in the taco seasoning, sweetcorn, 120ml water, 175g Cheddar cheese and the cooked rice.
Cook and stir until the cheese has melted and the sweetcorn is hot. Spoon the mixture into the flour tortillas. Roll into a tight cylinder and pack into an 20x28cm or similar sized baking dish (it will be a tight squeeze). Pour the salsa over top and sprinkle evenly with 175g Cheddar cheese.
Bake in the preheated oven until the cheese topping has melted and is beginning to brown, about 10 minutes.