In a small sauce pan, combine soy sauce, pineapple juice, brown sugar, ginger, and garlic. Set over medium heat. In a small mason jar, combine corn starch and water.
Shake vigorously to combine, add to sauce mixture. Whisk to combine until suace has slightly thickened. Remove from heat to cool. Reserve 1/2 cup in a small bowl.
Meanhwile, cut beef tenderloin in to bite sized pieces. Place in to a medium bowl. Top with cooled teriyaki sauce, and allow to marinate for at least 30 minutes. If you marinate for more than 30 minutes, place back in to the refrigerator. I haven't marinated this for more than 30 minutes, and would suggest not marinating it for more than 1 hour.
To assemble, place 1/2 slice of bacon on a cutting board, top with marinated beef tenderloin. Top with water chestnuts and green onion. Wrap bacon around ingredients. Use a toothpick to secure.
Set a saute pan over medium heat, and sear rumaki for 1 minute on each side, getting as good a sear you can across the entire surface. Transfer to a foil-lined baking sheet, seam down. I like using a wire rack so any residual grease can cook out.
Bake at 400 degrees for 15 minutes or until bacon is cripsy. Allow to cool slightly before serving.
