Marinade the tuna steaks in garlic, balsamic vinegar and brown sugar for 30 minutes. Remove the tuna from the marinade.
Heat the olive oil in a large heavy base frying pan. Fry tuna steaks 3 minutes on each side. Add in the cherry tomatoes and sizzle for 2 minutes. Add in the basil leaves and the crushed pepper flakes. Add in the reminaing marinade and sizzle into a thick syrupy glaze. Season with salt and pepper. Serve hot.
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