The idea of using mustard in various forms was inspired by Indian recipes. The spicy mustard oil and the popped black mustard seeds might be a little overwhelming for your first crop of haricots verts, but it’s a perfect treatment for large supermarket beans whose flavor is not quite so delicate. A garnish of yellow mustard flowers, if they can be found, would complete the theme and be quite enchanting with the green beans and black mustard seeds.