Preheat oven to 350 degrees. Place pecans on a rimmed baking sheet; toast until fragrant, 6 to 7 minutes.
Set a steamer basket in a large saucepan. Fill with enough water to come just below basket; bring to a simmer. Place green beans in basket; cover, and steam until crisp-tender, 5 to 7 minutes. (Alternatively you can use a microwave safe steamer bowl with vented lid or buy a frozen steamer bag of green beans.)
Transfer green beans to a serving platter; drizzle with oil, season with salt and pepper. Serve topped with pecans.