Preheat the broiler. Bring a large pot of salted water to a boil. Add the pasta and cook until al dente (about 2 minutes less than the label directs). Drain and rinse under cool water; shake off the excess. Transfer to a large bowl and set aside, stirring occasionally to prevent clumping, while you make the shrimp.
Toss the shrimp on a baking sheet with 1 tablespoon olive oil, the garlic, and salt and pepper to taste; arrange in a single layer. Broil the shrimp, turning once, until opaque and just cooked through, 2 to 3 minutes.
Add the shrimp, lemon zest and juice, scallions, mint, dill, cucumber, feta, olives and the remaining 1/3 cup olive oil to the bowl with the pasta; toss. Serve immediately or refrigerate, covered, up to 6 hours. (Bring to room temperature before serving.)