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.

Shopping Tips:

Look for quick grits near oatmeal and other hot cereals or near cornmeal in the baking aisle.

Shrimp is usually sold by the number needed to make one pound. For example, "21-25 count" means there will be 21 to 25 shrimp in a pound. Size names, such as "large" or "extra large," are not standardized, so to be sure you're getting the size you want, order by the count (or number) per pound. Both wild-caught and farm-raised shrimp can damage the surrounding ecosystems when not managed properly. Fortunately, it is possible to buy shrimp that have been raised or caught with sound environmental practices. Look for fresh or frozen shrimp certified by an independent agency, such as Wild American Shrimp or Marine Stewardship Council. If you can't find certified shrimp, choose wild-caught shrimp from North America--it's more likely to be sustainably caught.