Cook the Onions
In a large pot or Dutch oven, heat the olive oil over medium-high heat. Add the diced onion and cook, stirring occasionally with a wooden spoon, until the onion becomes translucent and begins to brown at the edges, approximately 5 to 7 minutes.
Add and Break Down the Tomatoes
Using a fork, remove the whole tomatoes from the can and add them to the pot, leaving the juice behind. Season with salt and cook, stirring occasionally, until the tomatoes break down and their liquid reduces to a thick, jammy consistency, about 5 to 7 minutes.
Season and Cook the Turkey
Stir in the chili powder and cook for a few seconds until fragrant. Add the ground turkey, seasoning it with salt. Stir to combine, breaking up the meat with the spoon, but do not worry about fully cooking it yet. The turkey will continue to cook as the chili simmers. Add the reserved tomato juice to the pot.
Incorporate the Chipotle Peppers
Using a fork, add two or three chipotle peppers from the can to the pot, breaking them up with the spoon. Pour in all of the adobo sauce. Adjust the level of spice by adding more peppers if desired—the entire can can be used for a spicier chili. Fill the empty chipotle can with cold tap water, swirl it to collect any remaining sauce, and pour this into the pot. Stir the ingredients together.
Simmer the Chili
Bring the mixture to a simmer over medium-high heat, with small bubbles occasionally breaking the surface. Once simmering, reduce the heat to medium-low, cover the pot, and continue to cook, stirring occasionally, until the liquid has reduced and the tomatoes have broken down completely, about 20 minutes. The chili should be thick and glossy. If the chili appears too watery, uncover and simmer for an additional 5 minutes, stirring occasionally. Taste and adjust salt if necessary. Serve with shredded cheese, sour cream, and cilantro leaves, if desired.