Preheat the oven to 350 degrees F.
Brush a large baking sheet with 1 tablespoon olive oil. Place the cubed potatoes on the baking sheet, then roast in the oven until golden brown and tender, about 30 minutes. Remove the potatoes from the oven and set aside.
In a large, oven-proof skillet, heat 1 tablespoon olive oil over medium heat. Add the onion and garlic, then cook until the onions are soft, stirring often to prevent the garlic from burning, about 5 to 7 minutes. Add the kale, then cook for a few minutes more until the kale begins to wilt. Add the roasted potatoes, then stir everything together until evenly distributed.
In a separate bowl, whisk together the eggs, salt, and pepper. Pour the egg mixture into the skillet with the potato and kale mixture, gently stirring until the egg is evenly distributed.
Place the skillet into the oven and bake for 15 to 20 minutes or until the frittata is golden brown and puffy. Cut into pie-shaped pieces, and serve warm or at room temperature.