Boil stock in a large pan over high heat. Add next 3 ingredients. Reduce heat to low, cover pan and simmer 4-5 minutes. Add peas and simmer another 4-7 minutes. Transfer mixture to a blender and process until smooth; season with salt and pepper to taste. Heat oil in a heavy nonstick skillet over medium high heat. Sauté mustard seeds until they start to pop. Pour oil spice mixture over soup.