Heat oil in a small skillet and cook the onion until browned, about five minutes.
Transfer the onion to a lightly oiled slow cooker (at least 3.5 quarts). Add the cornmeal, salt, and 1/2 teaspoon of chili powder. Stir in boiling water. Cover and cook on Low for 6-8 hours, stirring often.
In a large bowl, combine the salsa, beans, corn, chiles, red onion, olives, and remaining 1 tablespoon chili powder. Set aside.
About half an hour before ready to serve, spread the bean mixture over the top of the polenta. Cover and continue to cook on Low until warmed through.
Serve garnished with cheddar cheese or monterey jack cheese, and crumbled tortilla chips.