Cook pasta according to package directions, omitting salt and fat; drain, reserving 3 tablespoons of pasta water.
While pasta cooks, snap off tough ends of asparagus. Remove scales from stalks, if desired. Cut asparagus into 1-inch pieces.
Combine asparagus and peas in a steamer basket over boiling water. Cover and steam 3 to 4 minutes or until asparagus is crisp-tender. Drain.
Combine steamed vegetables, green onions, salt, and olive oil in a large bowl. Add pasta, reserved pasta water, tomato, and lemon juice; toss well. Add tuna; toss. Sprinkle with freshly ground pepper.