For best results, prepare the polenta the day before you grill it so it has enough time to become firm and sliceable.
1 ½ cups fine yellow cornmeal
1 ¼ tsp. salt
1 Tbs. olive oil or butter, plus more oil for grilling
Lightly coat 9 x 5-inch loaf pan with nonstick olive-oil spray and set aside. In medium saucepan, combine 4 1/4 cups water, cornmeal and salt; whisk well. Cook polenta, whisking constantly, until it starts to thicken. Add oil or butter and cook over low heat, stirring with wooden spoon and adding more water if necessary, a tablespoon at a time, to keep polenta from becoming too thick, about 30 minutes. Scrape polenta into prepared pan and smooth top. Cool, then cover pan and refrigerate overnight.
Preheat gas grill to medium or prepare charcoal fire. When ready to grill, remove polenta from pan and cut into 1-inch-thick slices. Brush both sides with oil and grill for 3 or 4 minutes each side. Serve grilled polenta hot with grilled ratatouille.