1Heat oven to 400°F. Melt butter in 10-inch skillet over medium heat. Cook onion in butter 4 to 6 minutes, stirring occasionally, until tender.
2Cut cheese to fit bread. Spread each bread slice with Dijon-mayonnaise blend. Top each with onion, apple and cheese. Sprinkle with chives. Place in ungreased jelly roll pan, 15 1/2x10 1/2x1 inch.
3Bake about 5 minutes or until cheese is melted. Serve warm.