Preheat the broiler. Bring a pot of salted water to a boil. Add the orzo and cook until al dente, about 8 minutes. Drain, rinse with cold water and shake dry.
Meanwhile, toss the spinach, radishes, cucumber, onion, olives, mint, parsley and 1/3 cup each lemon juice and olive oil in a large bowl. Add the orzo and season with salt and pepper.
Toss the shrimp with the remaining 2 tablespoons each lemon juice and olive oil in a bowl. Arrange on a foil-lined broiler pan and broil until slightly pink, 1 to 2 minutes. Turn and broil until just cooked through, 2 to 3 more minutes.
Divide the salad among plates. Top with the shrimp, sprinkle with the feta and season with pepper.