Preheat an outdoor grill to medium-high heat.
In a large skillet over medium heat, sweat garlic and shallots in olive oil until shallots are softened, about 4 to 5 minutes.
Deglaze pan with orange juice and soy sauce. Bring to a boil. Transfer mixture to blender. Add miso, wasabi and mirin. Blend until smooth.
Season tuna steaks with salt and pepper. Sear tuna on grill, about 1 to 2 minutes per side for rare. Slice tuna and plate immediately on bed of white sticky rice and finely sliced radicchio and romaine. Drizzle with ponzu sauce.