Preheat grill pan to high and oven to 400 degrees F.
Drizzle racks with oil and season with salt and pepper. Grill lamb over high heat for 2 or 3 minutes on each side. Transfer to a baking sheet or broiler pan and place in hot oven. Cook 12 to 15 minutes, to 130 degrees F on meat thermometer for rare, 155 for well. Let meat rest 5 to 10 minutes before serving for juices to redistribute.
For the chard, heat a large skillet over medium high heat. Add oil and the onion and saute for 2 minutes. Then add the greens in bunches until they wilt down enough to fit in the pan. Add the vegetable stock and raisins. Season greens with salt, pepper and freshly grated nutmeg. Reduce heat to medium low and cook 10 to 15 minutes until greens are tender and no longer bitter.
Place cranberry juice concentrate and the tangerine zest and juice in a small saucepan and simmer together over low heat for 10 minutes. Strain and return to pan. Meanwhile, combine the cranberries and chicken stock in a bowl. Cover and microwave on high for 1 minute. Let stand 10 minutes to reconstitute the cranberries.
For the polenta, heat a medium saucepan over medium high heat. Add oil and pancetta. Brown pancetta a minute or 2 and remove from pan to a paper towel lined plate. Return pan to heat and bring 3 cups chicken stock to a boil. Add the polenta and stir constantly until mixture masses, 2 or 3 minutes. Remove polenta from heat and stir in sage, butter, pancetta bits, and season with salt and pepper. Reserve the chives for garnish.
Heat cranberries and stock to a bubble and remove from stove.
To serve, allow 1/2 rack of lamb per person. Separate chops into 1 or 2 rib sections and glaze with cranberry-tangerine sauce. Serve with sage and pancetta polenta garnished with chives and braised red chard.