1. Cook pasta in about 3 quarts boiling water over high heat until tender to bite, about 10 minutes. Drain, immerse in cold water, and drain when cool, about 3 minutes.
2. In large bowl, mix lemon juice, oil, and pepper. Add pasta, feta, and cucumber. Mix and season to taste with salt. Add calendula petals and nasturtium blossoms; mix gently.
3. Line a platter or plates with nasturtium leaves. Spoon salad onto leaves.