Adjust rack to top position and preheat oven to 425 degrees. Wash and dry all produce. Trim and thinly slice scallions, separating whites from greens. Zest and quarter lemon (quarter both lemons for 4 servings).

Trim, peel, and cut carrots on a diagonal into 1/2-inch-thick pieces. Toss on a baking sheet with a large drizzle of olive oil and a pinch of chili flakes, salt, and pepper. Roast, flipping halfway through, until lightly browned and tender, 20-25 minutes.

Meanwhile, melt 1 TBSP butter in a small, lidded pot over medium-high heat. Add scallion whites; cook until slightly softened, about 30 seconds. Add rice, a pinch of salt, and 3/4 cup water (11/2 cups for 4 servings). Bring to a boil, then cover and reduce heat to low. Cook until tender, 15-18 minutes. Keep covered until ready to serve.

Heat a large, preferably nonstick, pan over medium-high heat. Add pistachios and cook, stirring, until lightly toasted, 2-3 minutes. Transfer to a small bowl. Pat fish dry with paper towels; season with salt and pepper. Add a large drizzle of olive oil to same pan over medium-high heat. Add fish, skin side down; sprinkle with half the Tunisian Spice (use all for 4 servings). Cook until skin is crispy and fish is cooked through, 3-5 minutes per side. (TIP: Lower heat if spice starts to burn.) Turn off heat; transfer to a plate. Wipe out pan.

Heat pan used for fish over mediumhigh heat. Add stock concentrate, juice from 1 lemon wedge (2 wedges for 4 servings), and 1/4 cup water (1/3 cup for 4). Cook, stirring, until slightly reduced, 2-4 minutes. Remove from heat; stir in lemon zest to taste and 2 TBSP butter (3 TBSP for 4) until melted. Taste and season with salt, pepper, and more lemon juice, if desired.

Fluff rice with a fork; stir in pistachios and remaining lemon zest. Divide rice, carrots, and fish between plates. Top fish with sauce. Sprinkle with scallion greens. Serve with remaining lemon wedges on the side.