Combine the first 9 ingredients, stirring with a whisk.
Heat a large nonstick skillet coated with cooking spray over medium-high heat. Sprinkle chicken with black pepper. Add chicken to pan; cook 4 minutes. Turn chicken. Add onion; cook 4 minutes or until chicken is done and onion is tender, stirring the onion frequently. Cut chicken into 1/2-inch-thick slices. Combine chicken, onion, bell pepper, cheese, chickpeas, and spinach in a large bowl. Drizzle vinaigrette over salad; toss gently to coat.