Heat the olive oil in a large heavy-bottomed pot over medium heat until it shimmers and begins to smell nutty, about 1 minute.
Add the diced onion and sauté, stirring frequently, until translucent and fragrant, about 5 minutes. The onions should be soft and slightly golden at the edges.
Stir in the chopped carrots and grated ginger, cooking for another 3-4 minutes until the carrots start to soften and the ginger releases a bright, spicy aroma.
Pour in the vegetable broth, bringing the mixture to a gentle simmer. Cover partially and cook for 20-25 minutes, until the carrots are very tender and easily pierced with a fork.
Remove the soup from heat and use an immersion blender directly in the pot, or transfer in batches to a blender. Puree until smooth and velvety, about 1-2 minutes, being careful with hot liquids.
Stir in lemon juice and season with salt and pepper to taste. Re-blend briefly if needed to incorporate the seasoning evenly.
Ladle the soup into bowls, garnish with a drizzle of olive oil or a sprig of fresh herbs if desired, and serve hot for a bright, comforting meal.