Mesa Grill's Southwestern Potato Salad

1 1/2 cups prepared mayonnaise 1/4 cup Dijon mustard 2 tablespoons fresh lime juice 2 tablespoons chipotle pepper puree 1 large ripe tomato, seeded and diced 1/4 cup chopped cilantro leaves 3 scallions, chopped, white and green parts 1 medium red onion, thinly sliced 1/2 teaspoon cayenne 4 cloves garlic, finely chopped Salt and freshly ground black pepper 16 new potatoes, about 3 to 4 pounds, cooked, drained and sliced 1/2-inch thick