Roasted Garlic and Peppers Pizza

1 large head garlic, unpeeled
2 tablespoons olive oil
1 large red onion, cut into 1/2−inch−thick rings
1/3 cup oil−packed sun−dried tomatoes, drained, oil reserved
1 − 12 inch pizza dough shell (uncooked)
2 cups grated mozzarella cheese (about 6 ounces)
1/2 cup roasted red bell peppers…