How to Make It
Heat oil in a large Dutch oven over medium-high heat. Add half of chicken to pan; cook 3 minutes on each side, or until browned. Repeat procedure with remaining chicken; cool. Cut chicken into bite-sized pieces.
Reduce heat to medium. Add onion and next 3 ingredients (through chiles) to pan; cook 2 minutes, stirring frequently. Stir in broth, scraping pan to loosen browned bits. Return chicken to pan. Stir in fish sauce and squash; bring to a boil. Cover, reduce heat, and simmer 15 minutes, stirring occasionally. Add mushrooms; cook 5 minutes. Add spinach; cook, covered for 5 minutes, or until spinach is wilted and tender, stirring occasionally. Stir in coconut milk; cook 3 minutes. Stir in salt and pepper. Sprinkle green onions over soup. Garnish with lime wedge, if desired.