This is a quick and easy side dish for anything off the grill or out of the oven, from meats to fish and chicken. Make it ahead and serve at room temperature with or without the tomatoes. Or, warm the green beans in low oven before tossing with the parmesan and serving.
Bring a large pot of salted water to a boil. Add the beans and cook until they are bright green and tender to the bite, about 3 minutes.
Drain the beans and transfer them to a mixing bowl. Squeeze half a lemon over the beans and toss well. Add the olive oil and season with the salt and pepper. Taste for seasoning.
The beans can be prepared in advance up to this point. If you'd like to serve them warm, cover and heat in a low oven.
Before serving, toss the green beans with most of the parmesan cheese. Transfer to a platter and top with the remaining parmesan.