Heat olive oil in a large pot over medium heat. Add chopped onion and sauté until softened and translucent, about 5 minutes. Stir in the minced garlic and cook for another minute.

Add the chicken thighs to the pot. Season with salt and pepper. Sear the chicken for 5 minutes on each side until browned. This adds depth of flavor to the soup.

Next, add the tomatillos, jalapeños, and chicken broth to the pot. Bring everything to a simmer and let it cook for 20 minutes until the tomatillos are soft and the chicken is fully cooked.

Remove the chicken thighs from the pot and set them aside. Using a blender or an immersion blender, blend the soup until smooth and creamy. If the soup is too thick, add more broth to reach your desired consistency.

While the soup is blending, shred the chicken using two forks. Once the soup is blended, return the shredded chicken to the pot.

Stir in the spinach (or other leafy greens) and half of the cilantro. Cook for another 5 minutes until the greens are wilted and tender. Finish the soup with lime juice for a zesty kick.