1. Place a metal baking sheet in the oven on the middle rack and preheat the oven to 400°F. Chop garlic. Pick the mint leaves off the stems, chop roughly and set aside.
2. Place the spinach in a large microwave bowl and microwave 1-2 minutes, or until wilted. Toss with tongs and microwave another 1 min. if necessary. Transfer to a colander and press out as much moisture as possible. Meanwhile, heat the oil in a frying pan and fry the onions, garlic and salt (in moderation) and ground pepper for 5 minutes on low heat. Add the ground beef, and cook on medium heat, stirring frequently to break up any lumps, 10 minutes, or until meat is cooked through. Remove the pan from the heat and mix in 2/3 of the chopped mint.
3. Meanwhile, cut the puff pastry sheet into 4 pieces. Roll each piece into a 7x4 inch rectangle and then fold in the narrow ends to create a boat shape. Pinch the edges up slightly to create a rim. Transfer pastry to a sheet of parchment paper. Repeat with remaining pastry rectangles. Divide the ground beef among the 4 pastry ovals, top with the spinach and cheese and sprinkle with the sesame seeds.
4. Remove the hot baking sheet from oven and carefully transfer parchment paper with flatbreads to baking sheet. Return to oven and bake 20 minutes, or until flaky and golden. Sprinkle with the remaining mint and serve.
Per serving: 570 calories, 40g fat, 11g saturated fat, 44mg cholesterol, 298mg sodium, 34g carbohydrate, 3g fiber, 2g sugar, 21g protein