Heat the olive oil in a large saucepan over medium heat. Add the diced onion and saute until translucent, around 5 minutes. Add the mint leaves and cook an additional 3-5 minutes. Fold in the peas and cook for two minutes.
Now pour in the chicken stock and bring to a boil. Season with salt.
Reduce the heat and simmer until the peas are tender, about 10 minutes.
Puree the soup using an immersion or regular blender.
Transfer to a large bowl and cool in the fridge.
Serve chilled, topped with a dollop of plain Greek yogurt and a sprig of fresh mint.