To a small food processor, add the peeled red onion quarter, roughly chopped coriander, the parsley leaves, minced or finely chopped garlic, the chilli paste, one lemon juice, salt and pepper, white wine vinegar and olive oil. Bltiz 30 seconds, you want a little texture but not too coarse.
Place a griddle pan on high heat.
Coat the fish with olive oil on each side, season with salt and pepper on both sides. Place on your hot griddle pan and grill the fish until you see the white cooked part almost halfway up. Then flip over and cook other side for about the same time. Turn off heat and using a spatula or fish spatula lift the fish off the griddle and place on a warm plate.
Spoon on some of the room temperature Chimichurri Sauce, serve immediately. Garnish with parsley or coriander leaves and a wedge of lemon.