Assemble your ingredients.
Preheat the oven to 425 degrees.
In a large mixing bowl, toss together the Brussel sprouts, garlic, culantro (if using, wait to add cilantro or other herbs), annatto oil, harissa, and sea salt. Make sure that the Brussel sprouts are evenly coated with the seasoning mixture.
Dump the bowl onto a large rimmed baking tray and spread out the Brussel sprouts as much as possible to allow them to cook properly.
Sprinkle the bacon lardons on top of the Brussel sprouts and put the baking tray in the oven.
Set the timer for 30 minutes. Midway through, you have to rotate the baking tray to allow the Brussel sprouts to cook more evenly.
When the timer goes off, take the tray out of the oven and give the Brussel sprouts a good stir with a spoon. Now is the time to add any toasted almond slivers or additional herbs if you are using them.
Return the baking tray to the oven and cook for another 10 minutes.
Harissa Brussel Sprout Roast is a wonderful side dish for any roasted meat, works particularly well with pork.