Heat the oil in a Dutch oven or large soup pot over medium heat. Add the garlic, onions, bell peppers, carrots, celery, and sweet potato. Sauté for 5 to 7 minutes, until soft.
Add the turkey and cook until browned, 5 to 7 minutes, stirring often to break up the chunks.
Once the meat is browned, add 1 1/2 cups water, tomato sauce, diced tomatoes in their juices, chili powder, cumin, paprika, cayenne, salt, black pepper, and red pepper flakes. Bring to a boil, then reduce to a moderate bubble. Let cook, uncovered, until the chili thickens, about 45 minutes, stirring every so often so that the chili does not stick to the bottom. If the chili becomes too thick, add a little water to reach your desired consistency.
Toward the end of the cooking time, taste and adjust the seasonings as desired. Add more cayenne pepper for an extra kick and more salt and pepper as needed. Serve hot with desired toppings.
Lexi's original version of the chili calls for slowly simmering it (in lieu of my "moderate bubble") on the stove for 3 hours, adding more water as needed. Since I started cooking the chili later in the day (ahem, I was running late), I cooked it more quickly, which you will see reflected in the recipe directions.
TO ADD BEANS: Add 1 (15-ounce) can black beans and/or 1 (15-ounce) can kidney beans.
TO STORE: Refrigerate chili in an airtight storage container for up to 4 days.
TO REHEAT: Rewarm leftovers in a pot on the stovetop over medium-low heat or in the microwave.
TO FREEZE: Freeze chili in an airtight freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.