Position a rack in the center of the oven and heat the oven to 475° F. Line a heavy-duty rimmed baking sheet with parchment. In a medium bowl, toss the green beans with enough of the olive oil to coat generously, the salt, and a few grinds of pepper.
Turn the beans out onto the baking sheet and arrange them so that they are evenly spaced. If the beans cover the baking sheet sparsely, arrange them toward the edges of the baking sheet for the best browning. Roast the beans until they're tender, a bit shriveled, and slightly browned, about 15 minutes.
Return the green beans to the bowl in which you tossed them with the oil, or put them in a clean serving bowl. If they seem a bit dry, drizzle them with a little oil. Season to taste with salt, pepper, and lemon juice or another flavoring, if using.