Bring a large pot of salted water to a boil. Add the orzo and cook until al dente, about 8-10 minutes. Reserve ½ cup of pasta water, then drain and set aside.

In a large skillet, melt butter over medium heat. Add the shrimp in a single layer and cook for 2-3 minutes per side until pink. Remove shrimp and set aside.

In the same skillet, add more butter if needed, then add minced garlic. Sauté for 30 seconds until fragrant, being cautious not to let it brown.

Return the shrimp to the skillet with garlic. Add the drained orzo, reserved pasta water, fresh spinach, and lemon zest. Toss gently for 2-3 minutes until spinach wilts.

Taste and season with salt, pepper, and optional red pepper flakes. Serve immediately, garnished with lemon zest.