In a large pot, bring 4 cups water to a boil. Add kale and salt; cook 1 minute. Using a slotted spoon, scoop kale into a large bowl. When kale is cool enough to handle, squeeze out excess water; set aside.
Bring water back to a boil; add sweet potatoes. Simmer until crisp-tender, about 3 minutes. Using a slotted spoon, scoop sweet potatoes into a bowl; set aside.
Measure out 3 cups cooking water, discarding the rest, and pour it back into the pot. Bring water back to a boil, add quinoa, and stir. Reduce heat to medium-low, cover pot, and simmer until water is absorbed, about 12 minutes. remove from heat and set aside, covered for 10 minutes.
Add quinoa to bowl of kale and toss to combine. Gently mix in sweet potatoes, onion, Parmesan, dill and cayenne. Set aside to cool 10 minutes. Add eggs and mix to combine.
Set out a large, rimmed baking sheet. using a 1/2 cup measure, scoop quinoa mixture, press firmly to level the top, then turn cup over or baking sheet. Repeat to form 14 patties total. (At this point the patties can be covered with plastic wrap and refrigerated up to 1 day.).
In a large skillet, heat 2 Tbsp. olive oil over medium heat. Working in batches, cook 4 to 6 patties at a time until golden brown, about 4 minutes. Carefully flip the cakes and brown on the other side, about 4 minutes longer. Add more oil, as needed, to cook additional batches. Serve warm or at room temperature.