Preheat your oven to 425°F and position a rack in the upper-middle area where the beans will get direct heat. While the oven heats, trim the green beans and pat them completely dry with paper towels—this is crucial for achieving crispy edges rather than steamed beans. Grate your parmesan cheese fresh if you haven't already, as pre-grated cheese contains anti-caking agents that prevent it from melting smoothly and evenly.

In a large bowl, toss the trimmed green beans with the olive oil, coating them evenly. Add the freshly grated parmesan, garlic powder, salt, black pepper, and onion powder, then toss everything together until the beans are uniformly coated with the seasoning mixture. I like to use my hands for this step to ensure every bean gets a good coating of the cheesy seasonings—it makes a real difference in the final result.

Spread the seasoned green beans in a single layer on your preheated baking sheet, making sure they're in direct contact with the surface for maximum browning. Roast for 15 minutes until the beans start to blister and turn golden on the bottom. Remove the sheet from the oven, shake or flip the beans to redistribute them, then return to the oven for another 10 minutes until the other side is equally caramelized and the parmesan is melted and slightly crispy.

Remove the baking sheet from the oven and let the beans rest for just 1-2 minutes. Transfer them to a serving dish while they're still warm so the parmesan stays slightly crispy on the outside. Serve immediately to enjoy the best texture and flavor.