Ground turkey - Season with a generous amount of salt and pepper. Fold in cornstarch. (Can be done up to 1 day ahead).
Garlic / Onions / Sweet potatoes / Cilantro - Prep as directed. (Can be done up to 3 days ahead).
If slow cooking, heat up a skillet or saute pan over medium-high heat (if not slow cooking, heat up a Dutch oven). Add cooking oil and then garlic and onions with a dash of salt to heated oil. Saute until softened, ~3 minutes.
Fold in turkey and use a wooden spoon to break up into bits. Cook until brown, 5 to 7 minutes.
If slow cooking, transfer to slow cooker. Add in crushed tomatoes, cumin, paprika, chili powder, salt, chicken stock, and sweet potatoes and cook on low for 7 to 8 hours or high for 3 to 4 hours. (If not slow cooking, add all the same ingredients into the Dutch oven, cover, and bring to a boil. Then simmer uncovered for ~20 minutes.)
Once chili is done, season to taste with salt, pepper, any more of the spices, or dig into your condiments.
Portion into bowls and let everyone top with cilantro, avocado and sour cream. Scoop with tortilla chips if using.