Cook rice: Rinse rice in a fine-mesh sieve until water runs clear. Combine rice, 2 cups water, and 1 teaspoon salt in a medium saucepan and bring to a boil. Reduce heat to low, cover, and cook until rice is tender and water is absorbed, about 17 minutes. Fluff with a fork and keep covered until ready to serve.
Prep vegetables: Meanwhile, trim ends from celery, then thinly slice on an angle. Trim ends from snow peas. Squeeze ¼ cup lime juice into a medium bowl. Trim ends from scallions, then thinly slice.
Prep shrimp: Pat shrimp dry, then season with a pinch each of salt and pepper.
Make red curry dressing: Into bowl with lime juice whisk in half or all of curry paste, depending on your heat preferences, 2 tablespoons water, 4 teaspoons sugar, and 6 tablespoons oil until smooth. Season to taste with salt and pepper.
Cook vegetables: In a large skillet, heat 2 tablespoons oil over high. Add celery and snow peas along with ½ teaspoon salt and a few grinds pepper. Cook until crisp-tender, 3 minutes. Add shrimp to skillet and cook until slightly pink, 3 minutes more. Remove skillet from heat.
Finish & serve: Add half each of scallions and red curry dressing to skillet and stir to combine. Season to taste with salt and pepper. Serve rice topped with shrimp and vegetables. Drizzle with remaining red curry dressing and garnish with remaining scallions.