Cover cedar planks with water; soak 1 to 2 hours.

Preheat charcoal or gas grill for direct cooking over medium-high heat (375°). Pat salmon steaks dry with paper towels. Sprinkle both sides with ½ teaspoon salt and ½ teaspoon black pepper. Brush with 2 tablespoons olive oil.

Place salmon steaks on soaked cedar planks; place planks on grill rack. Grill 20 to 25 minutes or until salmon flakes easily with a fork (145°). If necessary, use a spray bottle filled with water to put out flare-ups.

For Chimichurri, place parsley, onion, remaining 6 tablespoons olive oil, lemon juice, vinegar, oregano, garlic, remaining ¼ teaspoon salt, and ¼ teaspoon black pepper, and crushed red pepper in food processor or blender. Cover and pulse or blend until coarsely chopped. To serve, top salmon with chimichurri. Garnish with fresh mint, if desired.