Peel and roughly chop the onion. Trim and roughly chop the celery. Trim and chop the aubergine into 2cm chunks. Halve the pepper. Scoop out the seeds and white bits. Roughly chop it.
Add the onion to a deep frying pan or wok with 2 tbsp water. Season. Cook over a low heat for 5 mins till the onion starts to soften. Stir often. If it looks like its going to burn, add more water.
Add the celery, aubergine and pepper to the pan with another splash of water. Pop on the lid. Cook for 8-10 mins till the veg look soft. Stir often. While the veg cook, peel and grate or crush the garlic.
Stir the garlic into the pan. Cook and stir for 1 min till the pan smells aromatic. Add the chopped tomatoes. Half fill the can with water. Add that to the pan. Put on the lid.
Bring the caponata to the boil, then turn the heat down. Simmer for 20 mins till the caponata is thick. Stir every so often to stop it catching.
Rub 1 tsp olive oil into each pork loin steak (both sides). Warm a non-stick griddle/frying pan on medium heat. Add the pork. Fry for 7-8 mins till the steaks are golden brown. Flip them over. Fry for another 4-5 mins till cooked through.
Put the pork on a plate. Cover with foil. Rest for 5 mins. Stir the Balsamic vinegar into the caponata. Taste and adjust the seasoning if you think it needs it.
Pick the leaves off the parsley sprigs. Serve the pork steaks with the caponata and the parsley leaves scattered over the top.