Son is living on organic yogurt, puréed soups and smoothies and doing pretty well.
Over the day, he drinks an entire lb of spinach or other greens and a cup of lentils (for iron). And has a couple of huge fruit smoothies. He liked the one he had last night quite a bit: 1 C frozen mango, 1 pint fresh raspberries, 2 bananas, a little water and a quarter cup of almonds.
For his green smoothies, I steam the greens for 5 or 10 minutes, then blend them into a drinkable liquid with half an avocado (for added calories).