Jamaican Kabocha Squash Soup

Name: Jamaican Kabocha Squash Soup
Ingredients: 1 pound kabocha squash (1/2 medium); 2 large carrots (about 4 ounces total); 1 small chayote (4 to 5 ounces); 1 small yellow onion; 2 large stalks celery (about 4 ounces total); 3 cloves garlic; 2 bone-in, skin-on chicken breasts halves (about 3 pounds total); 3 teaspoons kosher salt, divided; 3/4 teaspoon freshly ground black pepper, divided; 1 tablespoon olive oil; 3 quarts (12 cups) water; 2 shucked ears corn on the cob (fresh or thawed frozen); 8 ounces russet potatoes (1 small); 3 medium scallions, plus more for garnish if desired; 10 sprigs fresh thyme; 1 habanero pepper; 10 allspice berries; 1 (2.12-ounce) packet Grace Chicken Flavored Soup Mix; 1 cup all-purpose flour; 1/4 cup cold water