Crush peppercorns in spice grinder, food processor or in a mortar with pestle.
Pat peppercorns on both sides of Turkey medallions.
Refrigerate 30 minutes.
In large non-stick skillet, over medium heat, saute medallions in margarine and 1 teaspoon oil 4 to 5 minutes per side or until they are no longer pink in center.
Remove medallions from pan and keep warm.
Add remaining teaspoon of oil to skillet and saute onions 30 seconds.