Brush zucchini with oil. Grill for about 3 minutes per side or until dark grill marks appear and zucchini is still tender-crisp. Do not overcook or it will get soggy. Transfer to plate to cool.
Cut cooled zucchini on the bias into 1-in (2.5-cm) pieces. If not preparing salad immediately, transfer zucchini to airtight container and refrigerate for up to 2 days.
In large bowl, combine zucchini, tomatoes and pesto. Season with salt and pepper and stir to combine. Arrange salad on serving plate.
Rip cheese into bite-sized pieces and scatter on top of vegetables. Garnish with radishes and basil. Serve immediately.
Notes
Tip: Do not use a block of mozzarella for this recipe. Instead, opt for fresh mozzarella that is stored in water. It’s much more tender and has a milder, milkier flavour.