Cut one of the fennel bulb halves into 1/2-inch-thick wedges, and place on a parchment paper-lined baking sheet.
Trim tops from carrots and chop enough of the tops to equal 1 cup
Scrub carrots (do not peel) and add half of the carrots to the fennel wedges.
Add half of the scallions and 3 Tbsp olive oil. Sprinkle with 1/4 tsp salt & pepper.
Roast for 18 minutes, until carrots and fennel are completely tender and scallions begin to char, tossing occassionally. Remove from oven & cool to room temperature.
Thinly slice remaining carrots, fennel, and scallions diagonally into 3-inch-long pieces; place in a large bowl.
Add cooled roasted vegetables to raw vegetables in bowl. Add juice, cilantro, and carrot tops and toss.
Sprinkle with remaining 1/4 teaspoon each salt and pepper; drizzle with remaining 2 tablespoons olive oil, and top with feta and pistachios.
Serve immediately, or let stand at room temperature 1 hour.