Portobello and Black Bean Quesadillas

(8-inch) fat-free flour tortillas

Butter-flavored cooking spray

(4 1/2-inch) portobello caps, chopped

light balsamic vinaigrette

no-salt-added black beans, rinsed and drained

jar diced pimiento, drained

preshredded reduced-fat 4-cheese Mexican blend cheese

thinly sliced green onions

Salsa (optional)

Chopped fresh cilantro (optional)