Heat oil in a large non-stick frying pan over a medium-high. Add onion and garlic. Cook, stirring, for 3-5 minutes until onion is light golden.
Add carrot and mushrooms. Cook, stirring occasionally, for 10 minutes or until vegetables have softened.
Add tomato paste. Stir over heat a further 1 minute. Stir in tomatoes, water, stock cube and oregano. Bring to the boil. Reduce heat. Simmer, uncovered for 8-10 minutes or until mixture has thickened. Remove from heat. Stir in zucchini and basil.
Meanwhile, cook pasta in a large, deep pan of boiling water as directed on packet, until just tender (al dente). Drain. Return to same pan.
Add vegetable sauce and tuna to pasta. Stir to combine. Transfer to a large ovenproof dish. Top with bocconcini.
Bake in a hot oven (200 °C) for 20-25 minutes or until top is light golden. Garnish with extra basil leaves, if desired. Serve with a leafy salad.