Prepare the Dough: Mix the flour and salt together in a large bowl to start preparing the dough. Then, cut in the cold vegan butter or coconut oil using a pastry cutter or fork until the mixture resembles coarse crumbs. Gradually add ice water, one tablespoon at a time, until a soft dough forms. Next, shape the dough into a disk, cover with plastic wrap, and refrigerate for at least 15 minutes.
Make the Filling: While the dough chills, combine the fresh blueberries, lemon juice, lemon zest, honey (or maple syrup), and cinnamon in a small saucepan. Cook over medium heat, stirring frequently, until the mixture thickens slightly, about 5 minutes. Remove from heat and let it cool.
Assemble the Turnovers: Begin by setting your oven to 375°F (190°C) before assembling the turnovers. Roll out the dough on a surface dusted lightly with flour until it reaches an approximate thickness of 1/8 inch. Cut the dough into 8 equal squares. Using a spoon, add a dollop of the blueberry filling to the middle of each dough square. Then, fold each square diagonally to form a triangle, pressing the edges together firmly with a fork to seal.
Bake: Place the turnovers on a baking sheet lined with parchment paper before baking. Optionally, brush the tops lightly with almond milk for extra browning. Bake in the preheated oven for 20-25 minutes or until golden brown. After baking, take the turnovers out of the oven and let them rest for a few minutes. Finally, dust with powdered sugar before serving.