How to Make It
Cook pasta in a large pot of boiling salted water according to package directions for al dente. Drain and spread on a rimmed baking sheet. Toss with 2 tablespoons oil and set aside.
Whisk mustard, lemon zest and juice, garlic, salt, black pepper, and crushed red pepper in a large bowl. Whisk in remaining 4 tablespoons oil. Add cucumbers and feta and toss to coat.
Add pasta to cucumber mixture and toss to combine. Pasta salad can be made up to this point up to 2 days in advance. Just before serving, add cilantro and mint, drizzle with oil, and squeeze lemon half over top; toss and serve.