Griddled tuna stemperata

Name: Griddled tuna stemperata
Cuisine: Italian
Ingredients: 4 x 200g tuna steaks, each about 2cm thick; 1 tsp extra-virgin olive oil; 1 tbsp extra-virgin olive oil; 1 small red onion, finely chopped; 3 garlic cloves, finely chopped; Large sprig fresh rosemary, leaves picked and finely chopped; ½ tsp crushed chillies; 450g cherry tomatoes, halved; 3 tbsp red wine vinegar; 2 tbsp capers in brine, rinsed and drained; 75g pitted green olives, roughly chopped; 1 tbsp chopped fresh oregano; 1 tsp sugar; 2 tbsp chopped fresh flatleaf parsley