Add olive oil and sliced onion to a saucepan. Cover and cook until the onion softens.

Meanwhile, wash and dice the vegetables into small cubes. Add them to the saucepan and cook over low heat.

Halfway through cooking, add salt and a splash of water.

In a separate pot, bring water to a boil, add salt, then add the pasta. Cook according to the package instructions.

Drain the pasta while it's still al dente. You can either cool it under running water or pour it into a bowl that has been chilled in the freezer (it should be cold).

Toss the pasta quickly with a drizzle of olive oil. Check the vegetables—when they're cooked, transfer them to a large bowl to cool.

To assemble, add the pasta to the bowl with the vegetables. Adjust salt, add the cherry tomatoes, cheese, and basil, and mix well. Chill in the fridge for a couple of minutes before serving.