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