Heat a large skillet or wok over high until hot. Add oil and swirl to coat skillet. Add shrimp and stir until almost entirely pink, 1 to 2 minutes.
Add garlic and red-pepper flakes and stir until fragrant, 30 seconds. Add scallions and stir until bright green, about 1 minute. Add lemon juice and 2 tablespoons water.
Cook, scraping up any browned bits from skillet, about 1 minute. Season with salt and serve.
1 tablespoon coconut oil
1 pound large shrimp, peeled and deveined
2 garlic cloves, minced
1/2 teaspoon red-pepper flakes
2 bunches scallions, cut into 1 1/2-inch pieces
2 tablespoons fresh lemon juice