
3 (1-inch) slices Italian bread
¼ cup olive oil, divided
1 cup chopped onion
3 garlic cloves, minced
¼ teaspoon red pepper flakes
2 (28-ounce) cans whole tomatoes, undrained
¼ cup chopped fresh basil
1 tablespoon packed brown sugar
2 cups chicken stock
½ cup plain Greek yogurt
Salt and black pepper, to taste
2 tablespoons butter, softened
4 (½-inch) slices Italian bread
4 slices sharp Cheddar cheese