Combine first 6 ingredients in a small bowl. Spread about 1 1/2 tablespoons sour cream mixture onto each tostada. Top evenly with chicken and next 4 ingredients; serve with lime wedges.
*To make your own tostadas, brush or spray 4-inch soft corn tortillas with vegetable oil. Bake at 450°, turning once, 5 to 7 minutes or until golden brown.