Create the Spice Rub: In a small bowl, combine all the ingredients for the Cajun spice rub: both paprikas, garlic powder, onion powder, oregano, thyme, cayenne, salt, black pepper, and the optional brown sugar. Mix thoroughly until everything is evenly distributed.

Prepare the Chicken: Pat the chicken breasts completely dry with a paper towel. This is a crucial step for getting a good crust. Place them in a large bowl or a dish.

Season and Marinate: Drizzle the olive oil over the chicken breasts and toss to coat them evenly. Sprinkle the spice rub all over the chicken, using your hands to press the mixture firmly into the meat on all sides. Cover the dish and let the chicken marinate in the fridge for at least 30 minutes, or up to 4 hours for a deeper flavour.

Preheat the Grill: When you're ready to cook, preheat your outdoor grill or indoor griddle pan to a medium-high heat, around 200°C (180°C fan). You want it hot enough to sizzle, but not so hot that the spices burn before the chicken is cooked through.

Grill the Chicken: Place the marinated chicken breasts on the hot grill. Cook for 6-8 minutes on the first side. What works best for me is resisting the urge to move them around; this allows those beautiful, dark grill marks to develop.

Flip and Finish Cooking: Using tongs, flip the chicken breasts and cook for another 6-8 minutes on the second side. The chicken is done when it’s firm to the touch and the internal temperature reaches 74°C on a meat thermometer. Always check the thickest part of the breast to ensure it's cooked safely, as recommended by the Food Standards Agency.

Rest the Chicken: This is the most important final step! Transfer the grilled chicken to a clean cutting board and let it rest for 5-10 minutes before slicing. This allows the juices to redistribute throughout the meat, keeping it wonderfully moist.