To make the chili oil: Preheat an oven to 250 degrees F. On a sheet tray lined with foil, mix chili flake and ginger until well combined. Toast in the oven for 1 hour, stirring occasionally. Transfer toasted chili flake to a small pot and cover with oil. Simmer over the lowest heat setting for 1 hour until dark in color. Cool to room temperature, place in an airtight container (mason jars work well) and keep in the fridge for up to 1 year.

To make the soup: In a medium soup pot or dutch oven, heat the oil over medium heat. Slice the green onions, but keep the white/light green parts separate from the dark green parts. Add the white/light green parts to the oil with the chopped onion and carrot. Add the garlic, ginger and miso paste and stir to combine. Cook for 2 minutes, stirring regularly to prevent burning. Add the broth and bring to a simmer. Simmer for 5-7 minutes until the carrots are just barely tender. Add the udon noodles to the broth and cook for 4-5 minutes until tender. Add the chicken and simmer until the chicken is warmed through. Season to taste with salt and pepper. Transfer to bowls and top with remaining sliced green onions and chili oil to taste.