Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper and set aside.
Trim each Brussels sprout, and remove any dirty or brown outer leaves. Rinse them in a colander under cold water for 30-60 seconds to remove dirt. Pat dry and slice them in half lengthwise. Transfer to the lined baking sheet. Rinse and drain the chickpeas in the same colander, pat dry, and add them to the baking sheet.
Toss the sprouts and chickpeas in olive oil, salt, and pepper, spread them out in a single layer, and roast for 25-30 minutes, or until the sprouts are tender and slightly browned.
While they are roasting, prepare the farro according to package instructions. Whisk together the whole grain mustard, honey, and lemon juice, and set aside.
Divide the cooked Brussels sprouts, chickpeas, and farro into three bowls. Drizzle with dressing to taste and enjoy immediately. If you are not planning to eat them right away, store the ingredients and dressing separately in airtight containers in the fridge. Add the dressing right before you eat your bowl.