These crispy squares can also be lightly fried for a delicious appetizer or side dish.
Pour warm polenta into an oiled 8-by-8-inch square pan and smooth out top. Refrigerate until firm, at least 2 hours but up to overnight.
Preheat oven to 450 degrees. Flip polenta onto a cutting board. Brush the top with olive oil. Cut into 16 two-inch squares. Preheat a baking sheet for a few minutes and place the squares on the sheet.
Place baking sheet in the upper third rack of the oven. Cook 10 minutes. Meanwhile, make the tomato topping by combining all ingredients in a bowl and tossing to coat. Let sit until ready to serve.
Increase oven setting to broil and cook polenta squares until golden brown on top, about 3 minutes. Transfer squares to a platter and scatter tomato mixture on top.