Mix chicken, egg, breadcrumbs, Parmesan, half the garlic, 1/2 teaspoon salt, and pepper just until combined. Roll into 32 meatballs, about 1 inch across.
Heat oil in 6-quart pot over medium. Cook onion and carrots 5 minutes, then remaining garlic 30 seconds.
Add broth and remaining salt; cover and bring to gentle simmer. Add meatballs individually; gently simmer 5 minutes.
Add couscous; simmer 10 to 12 minutes until tender and largest meatball 165°F, stirring carefully between meatballs.
Add escarole; simmer 2 to 3 minutes until tender. Stir in lemon juice; divide among 6 bowls.