Cook pasta to al dente as per the package directions; drain and set aside to cool.
Meanwhile, cut avocado into cubes and slice tomatoes in half; toss into a large mixing bowl.
Add cooled pasta to mixing bowl along with crumbled feta, walnuts, chopped parsley, olive oil, juice of the lemon, salt and pepper. Toss to fully combine. Serve at room temperature or chilled with grapes on the side.