Place a rack in the center of your oven and preheat the oven to 425 degrees F. Place the green beans in the center of a large, rimmed baking sheet. Drizzle with the oil and sprinkle with salt, and pepper and toss to coat evenly. Spread the green beans into a single layer. It's OK if the sides touch, but make sure none of them are stacked on top of each other (if they do not all fit in a single layer, divide them between two baking sheets and bake on the upper- and lower-third over racks). I find if I put my mind to it, I can get 1 pound on an 11x17-inch baker's half sheet.
Roast the green beans for 15 without disturbing them, then likely shake the pan to turn them a little bit and expose the browning undersides. Return to the oven and continue roasting for 5 to 7 minutes more, until they are crisp-tender when pierced with a fork and have dark spots.
If using almonds, while the green beans roast, toast them in a small, dry saucepan over low heat, stirring often, until they are lightly golden and fragrant, about 5 minutes. Once they are toasted to your liking, immediately remove to a plate or bowl to stop their cooking.
Sprinkle the Parmesan and toasted almonds over the green beans. Enjoy immediately, with additional salt and pepper to taste.
TO STORE: Refrigerate green beans in an airtight storage container for up to 4 days.
TO REHEAT: Rewarm leftovers on a baking sheet in the oven at 350 degrees F or in the microwave.
TO FREEZE: Freeze leftovers in an airtight, freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.