Heat a large pot over medium heat.
Add the olive oil, 1 cup of the chopped scallions, and the minced garlic; sauté for 2–3 minutes until softened.
Add the diced tomato and cook 1 more minute, until the tomato softens.
Pour in the chicken broth, then stir in the cumin and chipotle chile powder (if using). Bring to a boil.
Reduce heat to low, cover, and simmer for about 15 minutes.
Divide the shredded chicken, diced avocado, remaining scallions, and chopped cilantro among four bowls (about 1/2 cup chicken and 1/2 avocado per bowl).
Ladle about 1 cup of the hot broth over the contents of each bowl, season with salt and pepper to taste, and serve with a lime wedge.