Steam the green beans in covered dish with a few tablespoons of water in the microwave for 3 minutes and set aside. Meanwhile, in a small saute pan, toast the pecans over medium-high heat, just until fragrant.
In a large bowl, whisk the mustard and 2 teaspoons water together. Drizzle in the olive oil to make an emulsion and season with salt and pepper. Toss the hot green beans in the mustard sauce. Place in a serving dish and top with the toasted pecans.