Wash green beans and Brussels sprouts; drain. Halve large Brussels sprouts. In a large saucepan cook Brussels sprouts in a small amount of lightly salted boiling water for 3 minutes. Add green beans; cook for 5 minutes more. Drain.
Drizzle vegetable mixture with olive oil. Sprinkle with salt and pepper. Roast, uncovered, in a 425 degree F oven about 20 minutes or until vegetables are crisp-tender and pancetta is crisp. Transfer vegetables to a serving platter. Squeeze juice from lemon over vegetables.