I'd been looking to find a recipe using Israeli Couscous (not easily found in our little rural town up until recently) and saw this being made on "America's Test Kitchen." It's a wonderful combo of textures and flavors -- hubby raved!
Bring vinegar, sugar, and pinch salt to simmer in small saucepan over medium-high heat, stirring occasionally, until sugar dissolves. Remove pan from heat, add shallots, and stir to combine. Cover and let cool completely, about 30 minutes. Drain and discard liquid.
Whisk oil, lemon juice, mustard, pepper flakes, and 1/8 teaspoon salt together in large bowl. Add cooled couscous, arugula, mint, peas, 6 tablespoons pistachios, 1/2 cup feta, and shallots and toss to combine. Season with salt and pepper to taste and transfer to serving bowl. Let stand for 5 minutes. Sprinkle with remaining 1/4 cup feta and remaining 2 tablespoons pistachios and serve.
For Israeli Couscous: Heat 2 cups of couscous and 1 tablespoon olive oil in a medium saucepan over medium heat, stirring frequently, until about half of grains are golden brown, 5 to 6 minutes. Add 2-1/2 cups of water and 1/2 teaspoon of salt; stir to combine. Increase heat to high and bring to boil. Reduce heat to medium-low, cover, and simmer, stirring occasionally, until water is absorbed, 9 to 12 minutes. Remove saucepan from heat and let stand, covered, for 3 minutes. Serve.