Remove stems of the romaine. Season with salt and pepper, drizzle with a olive oil and drop on the grill until grill marks appear, or about 30 seconds to 1 minute.
Zest the lemon and squeeze the juice into a medium mixing bowl. Mince the garlic, thinly slice the ginger, peel and slice the red onion and add into the bowl. Then add olive oil and regular oil, stir with a regular spoon. Taste and make sure the acidity and oil is in good balance; there should be neither an oily taste nor a sour one.
Season the tuna with salt, pepper and olive oil. Place on a hot grill and make the grill marks fast so as not to overcook the tuna. Remove from heat and slice thinly. Set aside.
Place the grilled romaine on a plate, place the tuna on top, drizzle the vinaigrette over it, add the wild arugula, scallion and the sliced radishes in the bowl and toss lightly, place on top of tuna. Enjoy!