In a medium bowl, mash the drained sardines with a fork until finely flaked.
Stir in the cooked kasha, large egg, hemp hearts, finely diced yellow onion, and half of the sea salt and black pepper until well combined.
Form the mixture into two or three thick patties, pressing firmly together to ensure they hold their shape during cooking.
Heat half of the olive oil in a non-stick skillet over medium heat and sear the cutlets for 4-5 minutes per side until a deep golden-brown crust forms.
Remove the cutlets from the pan and set aside; add the remaining oil to the same skillet.
Add the minced garlic and kale to the pan, sautéing for 3-4 minutes until the greens are wilted and tender.
Season the greens with the remaining salt, pepper, and lemon juice.
Plate the sautéed greens, top with the crispy kasha cutlets, and garnish with a dollop of Greek yogurt and crumbled feta cheese.