Bring 3-4 tablespoons water to a boil in a large, deep sided pan. Add the slivered greens. Cover and turn heat to medium low, and steam until the greens are tender but still retain their color, 4-5 minutes. If using spinach, you need only a minute or two.
To puree the greens: do this in batches. Place about 2 T water and about 2 cups of cooked greens in a blender. Don't use any more water than necessary to achieve a smooth puree.
Place the pureed greens in a sieve about 2.5 centimeters / 1 inch in diameter. Rest the sieve over a tall tumbler to catch the drippings. With the back of a large spoon, press down on the greens to squeeze out moisture. About a cup of liquid will be released into the tumbler. When no more moisture comes out, set the greens aside.
Heat oil in a skillet over medium low heat. Add mustard paste and green chilli and stir a few times, keeping the skillet partially covered if the mustard paste starts to splatter. Add the greens and salt and stir a few times. Add coconut and mix well. Remove from heat. Serve about 2 tablespoons per person on top of boiled rice.