Add garlic, oil, and a pinch of salt to a small pan over low heat. Cook for 10 minutes, stirring occasionally, until the garlic softens when mashed with the back of a spoon.
Remove the pan from the heat and add the tasted sourdough chunks to the hot oil. Toss the bread around until well coated, then transfer the bread to a large bowl.
Mix together the tomatoes, lemon zest, lemon juice, capers, parsley, basil, feta and chilli flakes. Add garlic oil once cooled. This may sit for a few hours before serving.
Right before serving, add the bread to the tomato mixture.