Mix the ground coriander, cumin, fennel, cayenne pepper and turmeric in a medium mixing bowl. Season both sides of each chicken breast generously with the spice mixture and sprinkle with salt and pepper. Save any of the remaining spice mix for a later use. Drizzle with a little olive oil and rub the spice mixture to coat the entire surface of the chicken breasts. Lay the chicken breasts on the grill and cook until brown grill marks form and the chicken is just cooked through, about 2 minutes per side. Transfer the chicken to a plate and let rest for 2 minutes.