In a large stock pot or dutch oven, saute onion, curry paste, garlic, ginger, bell pepper, and shiitake mushrooms in oil over medium heat until softened.
Add chicken broth and bring to a simmer. Add chicken thighs. Simmer on low for 15-20 minutes or until chicken is cooked through. Remove chicken with a pair of tongs, and set aside until cool enough to handle. Pull chicken into pieces, and set aside.
Add coconut milk, curry powder, brown sugar, and red pepper flakes to soup. Simmer until coconut milk has melted completely.
Add chicken back to soup and simmer for 15 minutes.
Ladle into bowls, and serve.
For garnish: Top with chopped green onions, cilantro, serrano pepper slices, edamame, sunflower sprouts, basil, mint, enoki mushrooms and a one wedge of lime squeezed over the top.
You can substitute noodles, shredded carrots, or ingredients of choice for the garnish.