Heat the olive oil in a large stock pot.
Cook the garlic, onion and scallion over medium heat for about 3 minutes until softened.
Whisk the flour and chicken broth together.
Pour the chicken broth into the pot, and turn the heat up to "high." Put the lid on the stock pot and bring the broth to a boil.
When the pot boils, add the spinach and turn the heat down to "medium-low." Allow the soup to simmer for about 15 to 20 minutes with the lid on.
Use an immersion blender to liquify the vegetables.
Add the milk, salt, and pepper.
Top each bowl of soup with about 1 tablespoon of Greek yogurt, for a little extra protein and acidity.