Place your fully-thawed shrimp in a colander to drain off any liquid and pat them dry with paper towels. Set aside.
Heat 1 tablespoon olive oil in a large, deep skillet over MEDIUM-HIGH heat. Add the shrimp to the skillet, season lightly with salt and pepper, and spread it out in an even layer. Cook for 1 to 2 minutes per side, just until pink and opaque. Transfer to a plate, leaving any juices behind in the skillet, and cover loosely with foil.
Reduce the heat to MEDIUM. Add the chopped onion along with 1 to 2 teaspoons additional olive oil if needed. Cook for 3 to 4 minutes, stirring, until softened and translucent. Add the garlic and cook for about 30 seconds, just until fragrant.
Stir in the orzo and cook for about 30 seconds, stirring constantly, to lightly toast it.
Add the tomatoes, pour in the low-sodium chicken broth and add the lemon zest. Increase the heat as needed to bring to a gentle simmer. Reduce the heat to MEDIUM-LOW, cover, and cook for 9 to 11 minutes, stirring once or twice, until the orzo is tender and most of the liquid has been absorbed.
Remove the skillet from the heat and stir in 1 tablespoon of the lemon juice. Add the shrimp back to the pan and gently fold to warm through.
Just before serving, fold in the feta and basil.
Serve warm, on its own or with a simple green salad or roasted vegetables.