Heat a large pot on medium heat. Add the oil and onion and stir for 2 to 3 minutes until the onion is slightly softened. Add the fennel seeds and garlic and stir until fragrant, about 2 minutes.
Add the broccoli to the pot, along with 1 teaspoon of salt and a pinch of pepper and stir. Pour in the vegetable stock and bring to the boil. Reduce heat to low and simmer until the broccoli is tender but still green, 12 to 15 minutes.
Add the tofu, seeds and herbs. Using a hand held stick / immersion blender (or transfer to a food processor), blend until it is completely smooth and silky in texture. Season with sea salt and black pepper.
The soup can be eaten hot, warm or chilled. To chill, cool it completely at room temperature and then place in the fridge and chill until ready to eat. To serve, ladle cold soup into bowls, add a few ice cubes and top with a scattering of seeds