Heat the sunflower oil in a wok, add the carrots, radishes and water and simmer for 2-3 minutes. Add the asparagus and mangetout, then stir-fry for 2-3 minutes, or until the vegetables are tender. Remove the vegetables from the wok and set aside.
Melt the butter in a frying pan until frothing and add the tuna steak. Sear each side for 1-2 minutes, depending on the thickness, until browned and cooked to your liking.
Pour the tamari soy sauce and honey into the wok and simmer for 1-2 minutes, then drizzle over the stir-fried vegetables.
To serve, spoon the stir-fried vegetables onto a serving plate, top with the tuna steak and garnish with a wedge of lime.