Preheat grill. Slice tenderloin down the middle lengthwise, leaving one long side connected so you can open it up like a butterfly. (Don’t stress if you accidentally cut it all the way through. Just grill the two pieces!)
Spread a little vegetable oil over the hot grill using tongs with an oil-soaked paper towel. (Towel should not be dripping with oil or it can cause high flames.)
Place prepared tenderloin on the hot grill and cook about 5-7 minutes on each side, until the center has reached at least 150 degrees F. Remove cooked meat to cutting board.
Gently stir all salad ingredients together. Serve within an hour (before avocado starts to brown).