HEAT greased grill to high heat.
BRUSH fish with oil. Grill 3 to 4 min. on each side or until fish flakes easily with fork.
MEANWHILE, melt butter in medium skillet on medium heat. Add leeks; cook and stir until tender. Add remaining ingredients; cook on low until cream cheese is melted and mixture is well blended, stirring frequently.
SERVE fish topped with sauce.