Pulse greens in a food processor or finely chop with a knife—they should be small but not puréed or mushy. Set aside.
Heat a large skillet over medium-low heat and add the oil, onion, and salt. Cook, stirring occasionally, until soft and lightly browned, about 10 minutes. Add the garlic, cilantro, and cumin seeds. Stir for 30 seconds.
Add greens to pan and sauté for a minute or two, until they have wilted. Turn the mixture into a large bowl. Let cool for five minutes, then add the breadcrumbs and feta. Mix well, then taste for seasoning. Add more salt if necessary—this is your chance to get the seasoning right while the mixture is egg-free.
Crack one egg into the bowl and mix with your hands to incorporate. Squeeze a small ball of the mixture. If it holds together, begin portioning out the remaining mixture into small balls. If it doesn't hold together, add another egg.
Heat oil in a skillet over medium-high heat. Add balls to pan—they should sizzle when they hit the oil—then turn heat down to medium or medium-low. Cook until golden, about 2 minutes. Use a fork to flip the balls to the other side and cook for another 2 minutes or so.
Serve immediately or at room temperature.