Place peppercorns in a medium-hot dry skillet and lightly toast for 3 – 4 minutes while stirring(releases flavor!). Add peppercorns to a small saucepan with oil, pepper flakes, garlic and onion. Bring to a boil while stirring. Remove from heat, stir in lemon and salt and allow to cool. Place in a jar and let stand at room temperature for 12 – 24 hours. Strain through coffee filter (optional). Brush fish with peppercorn oil and place on a white-hot grill for 3 – 4 minutes each side or until just a tad undercooked. Drizzle additional oil over and serve.