Pre-heat the oven to 200°C.
Rub the chicken breasts with half of the olive oil then season generously. Arrange on a lined baking tray and roast for 20 minutes. Check that it is cooked through, with no pink showing. Remove from the oven when ready, then transfer to a plate and allow to cool.
Meanwhile, heat the remaining olive oil in a large, heavy-based saucepan over a medium heat. Sweat the onion and garlic for 4-5 minutes, stirring occasionally, until softened and turning translucent. Add the chilli powder, oregano and seasoning, stirring well to combine thoroughly. Add the chicken stock, bring to the boil, then reduce to a simmer.
Shred the cooked chicken breasts and add back to the broth. Cover and reduce the heat to low. Simmer for 45 minutes, then stir in the sweetcorn and simmer uncovered for a further 5 minutes.
Remove from the heat and adjust the seasoning as necessary. Ladle into soup bowls and garnish with the crushed tortilla chips. Sprinkle a pinch of chilli powder on top if desired before serving.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.