3 tbsp. whole-grain mustard
½ c. olive oil
¼ c. capers
1 small shallot
1 c. quinoa
4 medium summer squash (zucchini and yellow squash)
1 c. fresh flat-leaf parsley
½ c. fresh mint leaves
4 inner celery leaves and stalks
½ c. roasted, salted pistachios, almonds, or hazelnuts
In a large bowl, zest the lemon (about 2 teaspoons), then squeeze in about 2 tablespoons juice. Add the mustard and 1/2 teaspoon each salt and pepper. Whisk in the oil, then stir in the capers and shallot; transfer half the dressing (about 1/2 cup) to a bowl and set aside.
In a medium heavy-based saucepan over medium heat, cook the quinoa, stirring occasionally, until toasted, 3 to 5 minutes. Add 1 1/4 cups water (it may spatter) and bring to a boil. Reduce heat and simmer, partially covered, for 12 minutes. Turn off the heat and let sit, covered, for 3 minutes more. Season with 1/4 teaspoon each salt and pepper. Fold in the reserved 1/2 cup dressing and let the quinoa cool.
While the quinoa is cooking, very thinly slice the squash and add to the bowl along with the remaining dressing. Let sit, tossing occasionally, for 5 minutes. Fold in the parsley, mint, celery, pistachios, and quinoa.