Heat the oil in a small pan and sauté together the garlic, onion and chilli. Remove off the heat and cool. Place the beef mince in a medium sized bowl and mix in the sautéed onion, garlic and chilli, along with the chopped coriander and fajita seasoning. Season with a little salt, divide into 2 and form into thick burgers. Next, heat up the remaining oil in a frying pan and cook the burgers on both sides till cooked through. Meanwhile, mix the caponata with the kidney beans and serve into 2 small bowls. When the burgers are cooked, split the burger baps and spread with the sour cream. Lay some salad leaves on the 2 bottom pieces and lay over a burger on each. Dress with some onion slices and jalapenos and place on the tops of the baps. Serve the Mexican chilli burgers on a wooden board with the kidney bean caponata on the side with warmed tortilla chips.