Cook the arborio rice: While the onions are cooking, combine the remaining 3 cups water and ¾ teaspoon salt in a soup pot or Dutch oven. Add rice and bring the water to a boil. Reduce heat to maintain a simmer, cover and cook for 15 minutes.
Reduce the heat to low, add 2 tablespoons water and cover the skillet (I used a baking sheet to cover mine). Cook until the onions are greatly reduced and have a deep caramel color, 25 to 30 minutes. Stir frequently while the pan is still hot and occasionally once the pan has cooled down (always recover the pan after stirring).
Caramelize the onions: Heat 2 tablespoons oil in a large skillet over medium-high heat. Add onions and ¼ teaspoon salt. Cook, stirring frequently, until the onions begin to brown, about 5 minutes.
First prepare the greens: Remove the ribs from the chard/kale and discard or save them for another recipe. Coarsely chop or tear the kale leaves. Trim any tough stems from the spinach/baby greens and roughly chop the leaves.