Step 1 Cook pasta in a large saucepan according to packet instructions, then drain, reserving 2/3 cup of the cooking liquid, and set aside.
Step 2 Meanwhile, heat olive oil in a large saucepan set over medium heat. Add onion and garlic; cook, stirring, for 5 minutes, or until soft. Add tomatoes and cook, stirring, for 5 minutes, or until just soft. Add cooked pasta and reserved cooking liquid; stir until liquid forms a thin sauce. Remove pan from heat and stir in basil.
Step 3 Place rocket, cucumber ribbons and olives in a salad bowl; drizzle with balsamic vinegar and toss.
Step 4 Divide caprese pasta among 4 plates, top with torn bocconcini and rocket salad, season with cracked black pepper and serve.