Cut potatoes, zucchini, broccoli and onion into small chunks and place in a 3-quart saucepan. Add pickles and chicken stock. Cover; bring to a boil.
Simmer 20 minutes or until vegetables are very tender. Puree in food processor or blender in 3 to 4 batches. Return to pan and heat through, or serve cold.
Season with salt and pepper. Serve with a dollop of yogurt.