PREP: Adjust rack to top position and preheat oven to 450 degrees. Line a baking sheet with parchment paper; coat parchment with nonstick cooking spray. Trim green beans if necessary.

CANDY: Heat 2 tsp water in a small pan over medium-high heat. Add brown sugar and a big pinch of salt; cook, stirring, until dissolved and beginning to bubble, 2-3 minutes. Add 2.5 oz pecans and stir to coat. Cook until syrup is thickened and coats pecans, 2-4 minutes. Transfer candied pecans to prepared baking sheet to cool and harden.

ROAST: Toss green beans on a second baking sheet with a drizzle of oil, salt, and pepper. Roast on top rack until browned and tender, 10-12 minutes. Transfer to a large bowl.

FINISH: Add garlic herb butter to bowl with green beans and toss to coat; taste and season with salt and pepper. Once cool enough to handle, crumble candied pecans over green beans before serving.