Cook the rigatoni in boiling water for 10–12 minutes, or according to the packet instructions, until al dente. Drain the pasta and rinse under cold running water, then drain again thoroughly and set aside to cool.
Meanwhile, heat a ridged iron grill pan over medium-high heat or set the griller to medium-high. Grill the capsicum halves, skin side up, for 5–10 minutes or until blistered and blackened. Place in a plastic bag, then leave until cool enough to handle.
Grill the onion and eggplant for about 2 minutes or until slightly charred. Turn them over so that they cook evenly. Add the zucchini, mushrooms and tomatoes to the grill, and grill all the vegetables for a further 2–3 minutes. Remove the pieces as they are ready. Place them in a large salad bowl.
Cut the eggplant slices into 2 cm strips. Peel the capsicum and cut into 2 cm strips. Add the eggplant and capsicum strips to the salad bowl, with the rocket. Mix in the pasta.
To make the dressing, mix the balsamic vinegar or lemon juice with the olive oil, basil, capers, garlic, if using, and pepper in a small bowl. Lightly toss this dressing into the salad. Sprinkle with shavings of Parmesan cheese and serve.