Heat oil in a 12 to 14 inch sauté pan with a lid. When hot, add onion and sauté for about 8 minutes, adding garlic during the last minute, stirring frequently. Add vinegar, brown sugar and most of the cranberries (reserve about 1-2 tablespoons for later).
Rinse greens and drain in a colander, then transfer greens to pan. Cook and stir (tongs work well) until wilted enough to cover with a lid. Cook, covered, stirring and turning occasionally, for 15 minutes, until greens are tender. Add another tablespoon or two of water if pan is drying up. Taste and season with a bit of salt and pepper. Stir in remaining cranberries (for a bright look). Sprinkle with pecans and serve.