Put a large pot over medium-high heat and add the vegetable stock along with the green lentils.
Bring the water to a boil and turn the heat down to medium.
Cook the lentils for about 15 minutes, without covering the pot, remove any foam produced by the lentils and stir occasionally.
Add the mushrooms and thyme to the pot, bring the heat down to a simmer, cover the pot with a lid and let it simmer for another 10 minutes.
Remove the stem, seeds and placenta of the bell pepper and dice the flesh.
Add the bell pepper to the pot, then make sure to stir well and let it simmer for another 5 minutes.
Turn the heat off and let the soup cool down for 5 minutes.
Divide between two bowls, serve with the optional toppings and enjoy!
Store the soup in an airtight container in the fridge, and consume within 2 days. Alternatively, store in the freezer for a maximum of 60 days and thaw at room temperature. The soup can be reheated in a pot or the microwave.