Heat a heavy-bottomed pot over medium heat and add olive oil, letting it warm until shimmering.
Add chopped onions and minced garlic to the pot, sautéing until fragrant and translucent, about 3-4 minutes. You’ll notice a sweet aroma and the onions will turn slightly golden.
Stir in diced chicken, cooking until it just starts to turn white around the edges, about 5 minutes. The chicken will begin to release some juices and smell savory.
Pour in the chicken broth, then stir in chili flakes. Increase the heat slightly and bring the mixture to a gentle simmer, watching the bubbles form and rise, about 2-3 minutes.
Lower the heat and let the soup simmer gently for about 20 minutes, stirring occasionally. The chicken will become tender, and the broth will develop a rich, slightly cloudy appearance with fragrant steam rising.
Taste the soup and squeeze in lime or lemon juice to brighten the flavors; add more chili flakes if you want extra heat.
Once ready, ladle the steaming soup into bowls, garnishing generously with chopped cilantro or parsley for a fresh, green burst.
Serve hot, enjoying the bold, spicy flavors and tender chicken in every spoonful.