Chill the chick peas and beans for as long as possible. Steep couscous in boiling salted water.
In a blender or food processor or by hand, blend until smooth the tahini paste, garlic, cumin, coriander, lowfat yogurt, parsley, olive oil, grated lemon zest and juice. Season to taste with salt and pepper and transfer to a mixing bowl.
Add the chilled beans to the dressing and walnuts. Fluff up the couscous with a fork and add to beans and walnuts; toss the ingredients together and adjust the seasoning.
On each dinner plate make an outer wreath of dressed greens, an inner wreath of mixed grilled vegetables of choice and center couscous and chick peas in the middle. Garnish top with roasted red peppers.