Place a steamer basket in a saucepan. Add water to just below the bottom of the steamer basket. Bring to boiling. Add asparagus and carrots. Cover and reduce heat. Steam for 5 minutes. Add yellow summer squash or zucchini. Steam for 4 to 5 minutes more or until crisp-tender. Transfer to a serving bowl.
Meanwhile, combine the lemon juice, melted margarine or butter, dill, and salt. Pour over the vegetables and toss lightly. Makes 4 servings.