Make the tomato salsa by mixing together all the ingredients in a bowl.
Put the sardines on a baking sheet and drizzle with the lemon juice. Season to taste with salt and pepper. Cook the sardines under a preheated hot grill, turning once, for 3–4 minutes or until cooked through.
Sprinkle with the chopped basil and serve immediately with the tomato salsa and toasted ciabatta.