Preheat oven to 400°. Coat a rimmed baking pan with cooking spray.
For dressing, in a large bowl, whisk together olive oil, mustard, honey, lemon juice, cider vinegar, garlic, salt and pepper.
Place pears into a second large bowl. Pour half of the dressing over the pears; toss to coat. Transfer pears to the baking pan. Roast until golden brown and just tender, 15 to 20 minutes.
Meanwhile, whisk mayonnaise into the remaining dressing. Add arugula, farro, goat cheese, and pecans. Toss to combine. Serve grain mixture topped with roasted pears.