Preheat oven at 400° Fahrenheit.
Cook turkey bacon by laying it on parchment paper lined baking sheet and adding it to oven. Bake for 7-9 minutes or until crispy. When ready set aside, discard of parchment paper and keep oven on.
Add peeled and cubed potatoes to medium pot with just enough water to fully cover potatoes. Bring to boil on high heat. Once boiling reduce heat to medium high and cook potatoes for about 10 minutes or until tender when poked with a fork.
While potatoes are cooking, add oil to small skillet on medium heat. Add chopped leeks and cook for 8 to 10 minutes, stirring often. Add minced garlic halfway.
Drain potatoes then add them to medium bowl. Mash cooked potatoes with butter until still a tad chunky.
Chop turkey bacon finely then add to potatoes along with cooked leeks, shredded cheese, chopped green onions, salt and pepper to potatoes and stir until combined. Set aside.
On large cutting board, dust all-purpose flour generously. Unroll puff pastry dough on top. With pizza cutter, cut 12 squares pieces of about the same size. (if dough is small, 8 to 10 squares)
Add 1 heaping tablespoon of mixture in the middle of each square. (optional step: keep little bowl with water close by, dip your finger tip, and add 1 drop of water to each corner.) Working with 1 corner at a time, pinch together opposite corners diagonally, then pinch together 2 other corners to create a pocket. Repeat until each square is filled.
Line baking sheet with parchment paper, and beat egg with 1 teaspoon water in small bowl. Transfer each filled puff pastry bite to baking sheet. Brush each puff pastry with egg wash generously, and bake for 21 to 24 minutes or until golden brown.
Let cool for a few minutes before serving.