In a 1 1/2-quart saucepan, mix the chicken, onions, chili powder, sugar, paprika, cumin, garlic powder and cayenne pepper; stir in the water. Cook over medium heat for 2 to 3 minutes or until thoroughly heated, stirring once or twice. For each quesadilla, spoon 1/2 cup of the chicken mixture on one half of a tortilla. Top with 1/4 of the avocado; sprinkle with 1 teaspoon lime juice. Top with 1/4 cup cheese and fold over. Press firmly. Coat the bottom of a 12-inch nonstick skillet with 1/2 teaspoon of the oil; heat over medium-low heat. Place one quesadilla in the skillet. Cook for 2 to 3 minutes or until golden brown, turning once with broad spatula. Repeat for the remaining quesadillas. Cut the quesadillas into wedges to serve. Garnish each wedge with the sour cream.