Finely dice the yellow onions and red bell pepper, then mince the garlic.
Heat the vegetable oil in a Dutch oven over medium heat, then add in the chopped onions and bell peppers with a pinch of salt. Sweat the vegetables until the onions are very soft and translucent, around 6-7 minutes. Add in the garlic and cook for one minute more.
Add in all of the spices—the chili powder, cumin, coriander, oregano, cayenne, and red pepper flakes—and cook for a few minutes until the spices are toasted and fragrant (do not burn).
Add around 1 ¼ pounds of the ground turkey to the pot and increase the heat to medium-high. Use a wooden spoon or spatula to break up the meat and cook for around 4-5 minutes, until no longer pink.
Stir in the beans, diced tomatoes, canned tomatoes, chicken broth, and salt until combined. Once boiling, lower the heat to a simmer and cook, uncovered, until the chili has thickened and intensified in flavor (around 1 hour).
In the meantime, season the remaining ¾ pound of turkey with a pinch of salt and pepper, then form the meat into teaspoon-sized balls. After the hour has passed, stir the prepared meatballs into the chili and simmer, stirring occasionally, until the turkey is just cooked and the chili has thickened (around 40 minutes). Add more broth if the soup gets too thick or sticks to the bottom of the pan. Taste and adjust the seasonings if needed, then serve.