Preheat the oven to 425 degrees. Wash and dry the brussel sprouts and trim their ends.Cut the bacon and fry it in a pan until crispy.Toss the brussel sprouts with olive oil, garlic powder, red chili pepper flakes, salt and pepper and roast for about 20 minutes, tossing them half way through.Crumble the bacon on top of the brussel sprouts, zest the lemon on top and sprinkle freshly grated Parmesan cheese. Mix and serve.