PARMESAN BREAD WITH TOMATO AND ONIONS

8 1/4-inch-thick slices ripe tomato
1 tablespoon olive oil
2 medium-size red onions, thinly sliced
(about 3 cups)
1 tablespoon balsamic vinegar
2 teaspoons chopped fresh thyme
1 1-pound loaf enriched frozen white bread dough, thawed
1/2 cup freshly grated Parmesan cheese (about 1 1/2 ounces)
1/4 teaspoon dried crushed red pepper, minced

Arrange tomato slices on rack. Sprinkle with salt. Let stand 30 minutes. Meanwhile, heat oil in heavy large skillet over medium-high heat. Add onions and sauté until very soft, about 15 minutes. Add vinegar and thyme. Sauté until liquid is absorbed, about 2 minutes. Remove from heat. Preheat oven to 375°F. Line 2 baking sheets with parchment paper. Place bread dough on lightly floured work surface. Knead cheese and red pepper into dough. Divide dough into 8 equal pieces. Form each piece into ball. Roll out each ball to 3 1/2-inch round. Arrange on prepared baking sheets, spacing evenly. Using spoon, make depression in center of each round. Spoon onion mixture into each depression. Top each with 1 tomato slice; press gently to secure. Bake until breads are golden, about 30 minutes. Transfer to rack and cool completely. Makes 8.