Preheat the oven to 200°C / 400°F / Gas Mark 6.
Wash the brussel sprouts, peel off the outer leaves, trim off the bottom of the core, cut in half.
Peel and core the pineapple, cut into 1.5 cm / 1/2 inch cubes.
Toss the brussel sprouts and pineapple with olive oil, lemon juice and balsamic vinegar. Season with salt and pepper to taste.
Spread in an even layer on a baking tray (without baking paper), roast for 15 minutes. The brussel sprouts shouldn't be overcrowded, so they can properly brown.
After this time, add the pecans and maple syrup, mix everything together and roast for 5 more minutes, until the brussel sprouts are browned and tender.
Serve and enjoy! Check if the brussel sprouts are sour enough, if not - sprinkle them with lemon juice.