Preheat broiler to high with rack about 4 inches from heating element. Line a baking sheet with foil and spray with non-stick cooking spray.

Arrange asparagus in a single layer on prepared baking sheet. Spray asparagus with non-stick cooking spray. Broil for 10 minutes, or until asparagus is charred and just tender, turning once halfway through cooking time.

While asparagus cooks, combine garlic and balsamic vinegar in small saucepan. Bring to a boil. Reduce heat and simmer for 5-7 minutes, stirring frequently, until vinegar is syrupy.

Drizzle vinegar over asparagus and season with salt and pepper.