Steam the potatoes in a steamer or over the stove for 20 to 25 minutes, or until just tender enough to smash (you don't want them to be mushy).
While the potatoes are steaming, add the rinsed lentils to a medium saucepan and thoroughly cover with water. Bring to a boil, reduce heat, and simmer, uncovered, for 20 minutes, or until firm-tender. If needed, add more water to keep the lentils submerged. Strain and set aside.
Preheat the oven to 400F. Line a large baking sheet with parchment paper or silpat.
Add the steamed potatoes and cooked lentils to a large mixing bowl. Use the back of a form to roughly mash (you want to retain quite a bit of texture). Add the rolled oats, kale, pepitas, chives, garlic, lemon juice, olive oil, paprika, sea salt, and black pepper. Thoroughly stir to combine, ensuring all ingredients are evenly dispersed. The mixture should be damp but able to hold its shape.
Use a 1/3-cup measuring cup to scoop out 1/3 cup of the mixture. Form the mixture into a patty that is 1-inch thick and just shy of 3 inches in diameter, and transfer to the lined baking sheet. Repeat with the remaining mixture. You should have 10–12 patties. (Note: the uncooked mixture is damp and can be a bit challenging to form into patties, but I promise they're worth the effort.)
Bake the patties for 23 to 25 minutes, or until the bottoms are golden-brown and they feel gently set but not firm.
Remove from the oven and cool completely on the pan before moving. They'll continue to firm up as they cool.