Preheat oven to 400°F. Brush bottom and sides of 10-inch cast-iron skillet with 1 Tbs. oil.Combine polenta, salt, and 3 cups water in saucepan. Bring to a boil, whisking constantly. Cook 5 minutes, or until polenta is thick. Spread polenta in prepared skillet, set in oven, and bake 20 to 25 minutes, or until beginning to brown on sides.Remove skillet from oven, and spread polenta with sauce. Top with half of goat cheese slices. Spread zucchini strips over goat cheese, top with bell pepper rings, then remaining goat cheese. Drizzle with remaining 1 Tbs. oil. Return to oven, and bake 10 to 15 minutes more, or until cheese is melted and bubbly. Cool 10 minutes before slicing and serving.