Coat a large nonstick skillet with cooking spray; place over medium-high heat until hot. Add onion; cook 5 minutes or until lightly browned. Add garlic; cook 30 seconds, stirring constantly.
Add spinach and next 3 ingredients; cook, uncovered, 20 minutes or until spinach wilts and most of the liquid is absorbed.
Heat tortillas according to package directions. Place about 1/2 cup chicken mixture on each tortilla. Top each with 1 tablespoon each of cheese, tomato and sour cream, and 1 teaspoon green onions.
Oxmoor House Healthy Eating Collection