Place the cashews and pumpkin seeds in a bowl and cover with water. Allow to soak while preparing remaining ingredients.
Cut the stem and inner seeds out of the poblanos and cut into 1-inch pieces. Place in a large saucepan. Peel and cut the potato into 1-inch pieces and add to the pan. Add the onion, fennel, herbs, spices and vegetable broth to the saucepan and bring to a boil. Reduce heat to a simmer, cover and cook until all the vegetables are soft, around 25 minutes. Remove from the heat to cool slightly.
Drain the soaked nuts and seeds. Pour into a blender and add the 1 cup of water. Blend at high speed to make a nut cream. When the mixture is smooth, add the cooked vegetable mixture. Vent the top of the blender lid and cover with a kitchen towel to allow heat to escape. Blend at high speed until mixture is smooth and creamy.
Pour the soup back into the saucepan and heat gently if the soup is to be served hot. If the soup is to be served cold, pour into a storage container and chill til ready to serve. Soup can also be served immediately at room temperature.
If desired, garnish the soup with grated Cheddar and pumpkin seeds.