1 medium seedless cucumber, peeled and cut into 1/4-inch dice
1 cup frozen petit peas, unthawed
3 tablespoons chopped frehsly flat-leaf parsley
1 1/2 tablespoons chopped fresh dill
In a medium saucepan, combine the rice with 3 cups of water and 1 teaspoon of salt and bring to a boil over high heat. Cover the saucepan, reduce the heat to low and cook for 18 minutes. Remove from the heat and let stand, covered, for 5 minutes. Fluff the rice and transfer to a large rimmed baking sheet to cool completely.
In a small bowl, combine the lemon juice, shallots and mustard. Whisk in the oil in a thin, stead stream. Season with salt and pepper.
In a bowl, toss the rice with the cucumber, peas, parsley and dill. Just before serving, stir in the dressing; season with salt and pepper.
The rice and dressing can stand at room temperature for up to 3 hours.