Polenta Toasts with Balsamic Onions, Roasted Peppers, Feta, and Thyme

Polenta with onions can be prepared in a few days.
In a medium saucepan, bring 3 cups of water and 1/2 teaspoon of salt to a boil. Gradually add the polenta, stirring constantly with a whisk. Reduce the heat to low and cook for 20 minutes, stirring frequently. Add 1 tablespoon of vegetable oil and 1 tablespoon of butter. Place the polenta in an 8-inch square glass or ceramic baking dish greased with cooking spray. Wrap the surface of the polenta in plastic wrap; refrigerate for 2 hours or until set.Preheat a large skillet over medium-high heat. Add the remaining 1 tablespoon butter and the remaining 1 tablespoon butter; stir to coat. Add garlic; simmer for 15 seconds. Add the remaining 1/4 teaspoon salt, the onion, and a sprig of thyme; simmer for 3 minutes or until the onion begins to soften. Reduce the heat to low; cook for 30 minutes or until the onion is very soft, stirring frequently. Add the vinegar; cook for 5 minutes, stirring frequently. Discard the thyme sprig.Place the polenta on a cutting board; cut into 16 squares. Cut each square in half diagonally. Preheat a large skillet over medium-high heat. Lightly brush the polenta triangles with cooking spray. Place 16 triangles in the pan; cook for 5 minutes on each side or until lightly browned. Repeat the procedure with the remaining triangles.Spread the onion mixture, bell pepper, and feta evenly over the triangles. Garnish with thyme leaves.