Heat a large heavy-bottomed pot (Dutch oven) over medium-low heat. Add the olive oil then the onions, peppers, garlic, cumin and 1 teaspoon kosher salt. Cook, stirring occasionally, until the vegetables have softened, about 3 minutes.
Add the ground turkey and cook, breaking it apart with a spatula, until it is no longer pink, about 5 minutes.
Add the diced tomatoes, pinto beans, tomato soup, water and pumpkin purée, stirring to combine.
Simmer the chili over low heat until it is warmed throughout and thickened slightly, 20 to 25 minutes. Season to taste with salt and pepper.
When ready to serve, top the chili with sour cream, cheese and scallions.