Preheat the oven to 425 degrees . In a resealable plastic bag, rub the pork chops with two-thirds of the garlic and 2 tablespoons olive oil; refrigerate. In a glass baking dish, combine the onions, vinegar, 2 tablespoons olive oil and 1/2 cup water. Cover and bake until the liquid is almost completely reduced, about 50 minutes; season with salt and pepper.
Meanwhile, in a medium saucepan, combine 2 cups water, the lentils, rosemary and remaining garlic. Bring to a boil, then lower the heat and simmer until the lentils are tender and the liquid is absorbed, about 25 minutes. Stir in 1 tablespoon olive oil; season with salt and pepper.
In a large skillet, heat the remaining 1 tablespoon olive oil over medium-high heat. Add the pork chops and cook, turning once, until golden and just cooked through, about 8 minutes; season with salt and pepper. Serve the pork chops on a bed of lentils, topped with the onions.