Combine the flaxseeds and water in a small bowl; set aside for 10 minutes until the mixture forms a gel, then mix well. While the millet is cooking, combine the carrots, scallions, basil, lemon juice, lemon zest, salt, and pepper in a large bowl. Once the millet is cool, add it to the bowl with the flaxseed mixture and mix well. Using your hands, shape the mixture into six burgers. In a large skillet, heat the oil over medium heat. Place the burgers in the pan and cook until golden brown, 7 to 8 minutes on each side. Serve warm wrapped in lettuce leaves with a dollop of Mango Salsa and a drizzle of Cumin Cashew Cream Sauce on top. Uncooked burgers will keep for up to 4 days in the refrigerator or 1 month in the freezer, stored between pieces of parchment paper in a sealed container.