Peel and dice the beets into small cubes.

In a large pot, heat the olive oil over medium heat.

Add the chopped onions and sauté until they become translucent, about 5 minutes.

Stir in the diced beets and cook for another 5 minutes.

Add the vegetable broth to the pot.

Mix in the salt and black pepper.

Bring the mixture to a boil, then reduce the heat and let it simmer for 25 minutes.

Using an immersion blender, puree the soup until smooth.

Stir in the lemon juice just before serving.