Mash 2 slices bread and mild into paste in large bowl using a fork. Mix in ground 2 pounds turkey, ½ teaspoon salt, and ½ teaspoon pepper using hands.
Heat oil in a 12-inch skillet or pot over medium-high heat until shimmering. Add 3 diced onions and cook until onions are softened, about 3 minutes.
Add ¼ cup chili powder, ¼ cup tomato paste, 6 minced garlic, 1 Tablespoon cumin, 1 teaspoon oregano, and ½ teaspoon red pepper flakes and cook until vegetables are lightly browned, about 4 minutes.
Stir in turkey mixture, 1 pound at a time, and cook, breaking up any large pieces with wooden spoon, until no longer pink, about 3 minutes per pound (break up gently as ground turkey is usually pretty soft, so it doesn't become a "mash").
The bottom of your pan may develop a hard crust about now. Don't worry, just keep cooking everything until the turkey is not longer pink.
Transfer the turkey mixture to your slow cooker.
In the same skillet you cooked the turkey, turn off the heat and add 15-ounce can of tomato sauce. Stir , scraping up any browned bits or crust. The crust will soften and mix into the tomato sauce. Pour this sauce into the slow cooker.
Stir in 2-15 ounce beans, 28 ounces diced tomatoes with juice, 1 ½ cups broth, 3 Tablespoons soy sauce,1 Tablespoon brown sugar, and2 teaspoons chipotles, if using, into slow cooker. Cover and cook until turkey is tender, 4 to 6 hours on low.
Let chili settle for 5 minutes, then remove fat from surface using large spoon. Season with salt and pepper to taste and serve with toppings, if desired.