Place a rack in the upper position of the oven and preheat the oven to 425°F. Wash the greens beans, thoroughly dry, and then trim the ends.
In a mixing bowl, combine the olive oil and harissa. Add the green beans and toss to evenly coat. Sprinkle with the salt and toss again.
Transfer the green beans to a large, rimmed baking sheet (no need to grease), and spread into an even layer. Place on the upper rack of the oven and roast for 10 to 12 minutes, stirring once halfway through, or until the beans are lightly browned and look slightly shriveled. Remove the beans from the oven, and sprinkle with the almonds, if using.