Place poblano chiles on a foil-lined baking sheet. Broil 14 minutes or until blackened, turning twice. Place in a zip-top plastic bag; seal. Let stand 10 minutes; peel.
Heat a small saucepan over medium heat. Coat pan with cooking spray. Add carrot to the pan; cover and cook 5 minutes or until carrot is crisp-tender, stirring occasionally. Add water and next 5 ingredients (through bay leaves) to pan; stir well. Bring mixture to a simmer; cook 1 minute or until sugar dissolves, stirring frequently. Discard bay leaves. Combine onion and salt in a large bowl; pour vinegar mixture over onion mixture. Cool completely.
Place potato in a saucepan; cover with water. Bring to a boil. Reduce heat. Simmer 10 minutes or until tender; drain.
Heat a large nonstick skillet over medium heat. Remove casings from the sausage. Cook sausage for 10 minutes or until browned, stirring to crumble. Remove sausage from pan, reserving 1 teaspoon drippings in pan. Drain sausage on paper towels. Add potato to pan; cook 15 minutes, browning on all sides. Stir in sausage; cook until mixture is thoroughly heated.
Cut a lengthwise slit in each chile; discard stems, seeds, and membranes. Place about 1/2 cup sausage mixture in each chile (chiles will be full). Divide onion mixture evenly among each of 6 plates; top each serving with one stuffed chile. Garnish with cilantro, if desired.