Heat the oil in a large Dutch oven over medium-high heat. Add the onions, paprika, and cayenne and season with salt and pepper, to taste. Cook stirring occasionally, until the onions are softened, about 5 minutes. Add 1/2 cup water to the pot and once the water is simmering, add the greens (you may have to pack them in). Season generously with salt and pepper, cover with a lid and cook for 10 minutes. Remove the lid, toss the greens well with tongs, and continue simmering on low heat, until the greens are completely cooked and nearly all of the liquid has evaporated, about 10 minutes more.
Taste and adjust seasoning. Transfer to a serving bowl and serve warm.