Bring a large pot of salted water to a boil. Cook orzo until al dente, about 8 minutes. Drain and toss with 1 tbsp olive oil to prevent sticking.
Meanwhile, preheat grill or skillet to medium-high. In a bowl, mix lemon juice, 1 tbsp lemon zest, minced garlic, 2 tbsp olive oil, red pepper flakes (if using), salt, and pepper. Add shrimp to the glaze, toss, and grill for 2-3 minutes per side until pink and charred.
In a large bowl, combine cooked orzo, spinach, remaining lemon zest, 2 tbsp olive oil, dill, and half the feta cheese. Add grilled shrimp and sauté the garlic-lemon glaze (reserving a splash for drizzling). Toss to combine.
Adjust seasoning, garnish with remaining feta and dill, and serve immediately. Add a squeeze of fresh lemon just before serving.