Peel and thinly slice the Spanish onion into rings, then scatter them evenly over the tomatoes.

Using a food processor or blender, combine the basil, garlic, and pine nuts until coarsely chopped.

While the machine is running, slowly drizzle in the olive oil and lemon juice. Add salt and freshly ground pepper to taste and blend until the dressing reaches a smooth consistency.

Generously drizzle the prepared pesto dressing over the salad, ensuring an even coating across the ingredients.

Serve immediately, ideally accompanied by toasted ciabatta bread.