Clean and slice the fennel bulb, reserving any greens for garnish. Cook the fennel in the stock with the garlic and shallots until soft. Puree in a blender with the lemon juice and zest, and the spices. Strain the puree if you wish a smoother texture.
Combine well with the yogurt and chill. Serve garnished with chopped fennel greens or chopped cilantro.