Shrimp and Cheddar Grits

Position rack in upper third of oven; preheat broiler. Bring broth and water to a boil in a large saucepan over medium-high heat. Whisk in grits and 1/4 teaspoon pepper. Reduce heat to medium-low, cover and cook, stirring occasionally, until thickened, 5 to 7 minutes. Remove from heat and stir in cheese. Cover to keep warm. Meanwhile, toss shrimp, scallions, oil, garlic powder, the remaining 1/4 teaspoon pepper, and salt in a medium bowl. Transfer to a rimmed baking sheet. Broil, stirring once, until the shrimp are pink and just cooked through, 5 to 6 minutes. Serve the grits topped with the broiled shrimp and scallions.