To prepare the tomatoes, preheat the oven to 120 degrees Celsius and brush each tomato half with a mix of the two oils. Place in the oven and roast slowly for approximately 3 hours. The tomatoes will happily keep warm for longer if needed; just turn the oven down to 50 degrees Celsius.
While the tomatoes are roasting, place the tuna steaks in a dish and cover with the combined lime juice, olive oil, garlic, coriander and seasoning. Cover in plastic wrap and refrigerate for at least 1 hour.
Wash and top and tail the beans and place them in a steamer.
Heat the grill to hot and put the beans on to steam. Ensure that your barbeque or chargrill pan is well oiled so the tuna won't stick. Grill the tuna steaks for 2-3 minutes on each side, turning once only.
Remove the beans from the heat.
To serve, put some hummus on each plate, mix together the olive and chilli oil and drizzle a little over the hummus. Place three tomato halves on each plate, the beans on top of the hummus and the tuna on top of the beans.