Step 1

Heat oil in a large saucepan over medium-high heat. Add onion, mushrooms, celery and carrots; cook, stirring occasionally, until the vegetables start to brown slightly, about 6 minutes. Stir in garlic, sage, cayenne (if using) and bay leaf; cook, stirring constantly, for 1 minute. Stir in chicken, broth, salt and pepper.

Step 2

Bring the mixture to a boil over medium-high heat. Reduce heat to medium; simmer, undisturbed, until the chicken is fork-tender, about 20 minutes. Transfer the chicken to a plate to cool slightly, about 5 minutes.

Step 3

Meanwhile, stir kale into the soup; return to a simmer over medium heat. Simmer, undisturbed, until the kale is tender, about 5 minutes. Remove from heat.

Step 4

Remove and discard bones from the chicken; shred the chicken. Stir lemon juice and the shredded chicken into the soup.