Start by preheating your oven to 400 degrees Fahrenheit. While the oven is warming up, wash your green beans thoroughly and trim off the tough stem ends. It is very important to pat the beans completely dry with a clean kitchen towel or paper towels. Any moisture left on the beans will cause them to steam rather than roast, which prevents them from getting crispy.
Place the dried green beans on a large rimmed baking sheet. Drizzle them with the olive oil and add the minced garlic, salt, pepper, and onion powder. Use your hands or a pair of tongs to toss everything together until every bean is evenly coated with the oil and spices. Spread them out in a single layer, ensuring they are not overcrowded on the pan.
Slide the baking sheet into the center rack of the oven. Bake for about 15 minutes. At the halfway mark, use a spatula to toss the beans. This ensures that they cook evenly and get those delicious brown blister marks on all sides. You will notice the beans starting to soften and slightly wrinkle.
Remove the pan from the oven briefly. Sprinkle the grated parmesan cheese and panko breadcrumbs over the top of the beans. Gently toss one more time so the cheese and crumbs adhere to the oiled surface of the vegetables. Return the pan to the oven for another 5 minutes, or until the cheese has melted and the breadcrumbs are a beautiful golden brown.
Take the beans out of the oven and let them rest for just a minute. The cheese will crisp up slightly as it cools. Transfer them to a warm serving platter and serve immediately while the coating is still crunchy and the beans are tender.
