Preheat the grill to medium-high heat (approximately 400°F / 204°C).
Place the trimmed asparagus spears on a large rimmed baking sheet or in a shallow dish.
Drizzle with olive oil and sprinkle with salt, black pepper, and garlic powder.
Toss the spears thoroughly by hand to ensure an even coating of oil and spices.
Place the asparagus spears directly on the grill grates, positioned perpendicular to the bars to prevent falling through.
Grill for 6 to 10 minutes, turning halfway through with tongs, until the spears are tender and show visible char marks.
Remove from the grill and transfer to a serving platter.
Immediately drizzle with fresh lemon juice and sprinkle with the lemon zest.
Top with grated Parmesan cheese if desired and serve warm.