In a large stockpot, bring water and salt to a boil. Add greens, stirring to submerge. Return to a boil and boil, uncovered, 15 minutes, stirring occasionally. Drain greens in a colander.
While greens are cooking, heat olive oil in a 12-inch skillet. Add garlic, olives, cumin, pepper flakes (use larger amount if you like things spicier) and the zest from the orange. (To remove zest from the orange, use a microplane if you have it, otherwise, use a zester, or even a vegetable peeler to remove just the colored part of the skin, and then chop it very finely.) Cook the mixture and stir for a minute or so, just until garlic begins to color. Dont let garlic burn.
Add drained greens to the skillet and stir to combine with olive oil mixture. Add juice from the orange (about 1/4 cup), and brown sugar, and cook, uncovered, for another 5-7 minutes to evaporate remaining juices and concentrate the flavors.