Heat a splash of oil in a large heavy-bottomed pot over medium heat until shimmering, and the oil begins to ripple slightly.
Add chopped onions and minced garlic to the pot. Sauté, stirring frequently, until fragrant and the onions are translucent, about 5 minutes. The mixture should smell sweet and savory.
Stir in the ground turkey, breaking it apart with your spoon. Cook until the turkey turns a light golden brown and loses its raw pink color, about 8 minutes. The meat will start to brown on the edges and smell savory.
Add chopped bell pepper and chili powder to the pot. Stir well and cook, stirring occasionally, until the peppers soften slightly, about 5 minutes. Expect the mixture to become fragrant with a bit of smoky spice.
Pour in the canned diced tomatoes along with their juices, and add the drained kidney beans. Stir everything together and bring the mixture to a gentle simmer. The sauce will start to bubble and thicken slightly.
Reduce the heat to low, cover the pot, and let the chili simmer gently for about 30 minutes. Stir occasionally to prevent sticking and to help flavors meld. The chili should develop a rich aroma with smoky and spicy notes.
Uncover the pot and taste the chili. Adjust seasoning with salt, pepper, or extra chili powder for more heat. If the chili is too thick, stir in a splash of chicken broth to reach your desired consistency.
Let the chili rest off heat for about 10 minutes; this allows the flavors to deepen further. Give it a gentle stir before serving.
Spoon the hearty turkey chili into bowls, garnish with fresh cilantro if desired, and enjoy the comforting, flavorful dish with a warm slice of bread or your favorite sides.