For the dressing: Whisk together the yogurt, kefir, dill, oil, garlic powder, salt, onion powder and cayenne in a medium bowl. Allow to sit for 1 hour in the refrigerator to let the flavors mingle.
For the salad: Preheat a grill pan over medium-high heat.
Cut the radicchio into 8 wedges, then drizzle with the olive oil and sprinkle with salt. Place the wedges on the grill and cook until slightly browned and wilted, about 2 minutes per side. Place the wedges on a platter.
Meanwhile, quarter the romaine and nestle it in between the wedges of radicchio. Dollop the dressing around the platter and crumble the Gorgonzola over the top.