How to Make It
Heat oven to 400°F. Spread pecans on a rimmed baking sheet and bake, tossing once, until toasted, 6 to 8 minutes. Let cool, then roughly chop.
Bring a large pot of water to a boil and add 2 1/4 tsp. salt. Add green beans and cook until just tender, 4 to 5 minutes. Drain and run under cold water to cool.
In a large bowl, whisk together oil, vinegar, mustard, maple syrup, 1/2 tsp. salt and 1/4 tsp. pepper. Add green beans and pecans; toss to combine. Serve at room temperature or cold.