Step 1Saute onion in oil in large skillet over medium heat until tender, about 5 minutes. Add meat and saute, breaking up with spoon, until browned, about 5 minutes. Let cool.
Step 2Beat egg in large mixing bowl. Add cornmeal, milk and chili powder and mix. Add undrained tomatoes, undrained corn and meat mixture. Season to taste with salt. Turn mixture into greased 2 1/2-quart casserole.
Step 3Distribute olives over tamale mixture and poke in with tip of spoon. They must be completely covered so they won't burn. Bake at 325 degrees until center is done, 1 hour 15 minutes to 1 hour 20 minutes. Cool slightly before serving.