Heat the pot over a low heat and add the olive oil.
Add the onion and cook until translucent but not browned, stirring frequently. Add the garlic for the last couple of minutes of this step.
Add the broccoli and stock to the pot. Bring it to the boil then reduce to a simmer for 5 minutes.
Add 300g of the peas and simmer for another few minutes.
Take off the heat, add the spinach and mint into the pot, bit by bit, blending the soup as you go. If you want the soup to be smoother, you can use a food processor for this step.
Add in the rest of the peas and return to the heat for a few minutes, until the peas are heated through. Season with salt and pepper, to taste.
Divide the soup betwen four bowls and add a tablespoon of yoghurt to each. Add more chilli flakes, if you like heat. If you don't want to use the lemon yoghurt, I would add the lemon directly into the soup.