In a saucepan, melt the sugar & cider, vinegar.
Add the onion and ginger and simmer until the sugar thickens.
Add the green tomato and cook until the tomatoes are soft and it is not watery; it will depend on how green the tomatoes are. If they are half ripe they will have more water in them.
Add the cranberries and chill.
If you like a spicy chutney, add some crushed chilies when you add the tomatoes.
Salt and pepper the Ahi tuna and sear in hot oil for 1 minute on each side.
Slice it thinly.
Fan out the tuna on a bed of spinach and top with chutney.