Halve the avocado and use a teaspoon to scoop chunks of the flesh into a bowl. Gently mix all the other ingredients, except the fish, in with the avocado, set aside.
Heat a griddle pan until very hot. Season the fish with pepper, and salt if you want, then drizzle with a little olive oil. Griddle the fillets for 2-3 minutes on each side until charred and cooked through. Serve with the avocado salad.