Farro Salad with Oven-Roasted Grapes and Autumn Greens

seedless red grapes, seedless red

bunches Concord grapes

Greens such as baby kale, mixed small

Red onions, small

Rosemary, fresh

Farro

Salt and freshly ground pepper, Coarse

Olive oil, extra-virgin

Sherry vinegar or red-wine vinegar