Start by preheating your oven to 375°F (190°C). This temperature ensures the chicken cooks evenly and the topping crisps up nicely without burning.
Pat the chicken breasts dry with paper towels and season them generously with salt, pepper, garlic powder, and onion powder on both sides.
In a medium bowl, combine the mayonnaise, Dijon mustard, and shredded cheddar cheese. Stir until smooth and well combined. In a separate bowl, crush the cornflakes finely, then add them to the cheese mixture. Gently stir to combine, ensuring the cornflakes remain somewhat chunky for texture.
Lightly grease a baking dish with olive oil to prevent sticking. Place the seasoned chicken breasts in the dish in a single layer. Spread the cheddar and cornflake topping evenly over each chicken breast, pressing down lightly to help it adhere.
Place the baking dish in the preheated oven and bake for 25-30 minutes until the chicken reaches an internal temperature of 165°F (75°C) and the topping is golden brown and crispy. Optionally, broil for 1-2 minutes at the end for an extra golden finish, watching carefully to prevent burning.
Once baked, let the chicken rest for a few minutes before serving. Serve with your favorite sides like roasted vegetables, salad, or mashed potatoes.