Heat the oil in a large, heavy-bottomed pot over medium heat. Add the onions and sauté until softened, 3-4 minutes. Add the ground beef or turkey and cook until browned, stirring frequently and breaking it up as you stir. Drain any excess grease, and then stir in the chili powder and cumin and cook for 30-60 seconds more. Add the remaining ingredients (including the juices from the tomatoes), stirring to combine. (Tip: I add 1/4 to 1/3 cup water to one of the tomato cans and swish it back and forth a few times among all 3 tomato cans. This way, you can get every last drop out of the cans.) Bring the chili to a boil, and then reduce the heat to medium-low, cover, and simmer for 15 minutes.