Place trimmed asparagus into a large bowl. Drizzle with the balsamic vinegar, olive oil, salt and pepper and garlic powder. Cover with plastic wrap and let marinate for 1 hour.
Preheat grill to medium heat.
Grill asparagus until tender crisp, about 6 minutes. Remove and let cool until room temperature. Sprinkle with the crumbled feta and the grape tomatoes.