Heat the olive oil in a medium saucepan over medium heat. Add the onion, garlic, and red pepper flakes. Cook, stirring occasionally until the onion is tender, about 6-7 minutes. Add the roasted red peppers and the vegetable broth. Bring to a boil, reduce the heat and simmer for 10-12 minutes.
Use an immersion blender to puree the soup until smooth, and season with salt.
Alternatively if you do not have an immersion blender, allow the soup to cool slightly then working in batches, puree the soup in a blender until smooth. Be careful to never fill the blender more than halfway each time so that the hot liquid and steam has room to expand. Reheat after blending and season with salt.
To serve, divide the soup among 4 bowls, top with millet salsa, squeeze a lime wedge over each bowl, and lightly drizzle with olive oil.