Prepare a medium fire in a charcoal grill,or preheat a gas or electric grill to medium.
In shallow baking dish,combine the oil,garlic,pepper flakes,and salt. Toss the asparagus in the seasoned oil to coat evenly.
Brush the grill with vegetable oil. Place the asparagus on the grate single layer. Grill,turning every 2 to 3 minutes,until grill-marked and tender,10 to 15 minutes. Transfer to a plate,sprinkle with the lemon juice,and serve.