1. Cook orzo pasta with 1 tablespoon kosher salt according to the package directions, omitting additional fat. Drain and rinse with cold water. Drain well.
2. Combine lemon juice and next 3 ingredients (through pepper) in a large bowl; stir well with a whisk. Add orzo, fennel, and the next 4 ingredients (through 1/2 teaspoon salt); toss well to coat. Cover and chill. Top with nuts before serving.