Boil a large pot of salted water and cook the orzo according to package instructions until al dente. Drain and set aside, reserving about 1/2 cup of the pasta cooking water.
In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Add the minced garlic and red pepper flakes, sautéing until fragrant (about 30 seconds).
Add the shrimp to the skillet and cook for 2-3 minutes on one side, until pink, then flip them over. Squeeze the juice of one lemon over the shrimp and season with salt and pepper.
Once the shrimp are cooked through, add the cooked orzo to the skillet along with the remaining tablespoon of olive oil, lemon zest, and the reserved pasta water. Toss everything together until well combined.
Gently fold in the spinach and parsley, cooking just until the spinach wilts. Adjust seasoning with salt, pepper, and additional lemon juice if desired.
Serve immediately, garnished with additional parsley and grated Parmesan cheese if using.
Notes
Adjust red pepper flakes and lemon juice to taste.