Heat the oven to 425ºF. Meanwhile, line a rimmed baking sheet with parchment paper or aluminum foil. Trim the stems ends from 1 pound green beans, then pat very dry.
Place the green beans, 2 teaspoons olive oil, 2 teaspoons finely grated lemon zest, 1 teaspoon lemon juice, ¾ teaspoon kosher salt, and ¼ teaspoon black pepper on the baking sheet. Toss with your hands until evenly coated, then spread into an even layer.
Roast for 5 minutes. Stir and arrange the green beans back into an even layer. Evenly sprinkle with 1 ounce grated Parmesan cheese.
Return to the oven and roast until the cheese and green beans are browned in spots, 5 to 6 minutes more. Transfer to a serving dish. Sprinkle with more grated Parmesan cheese, lemon zest, black pepper, and ½ cup toasted, sliced almonds if using.