Heat the oil in a large skillet over medium-high heat. Add the onion and cook for 3 minutes, or until wilted. Add the chicken and peppers, and cook for another 3 minutes. Stir in the fresh and canned pumpkin, tomatoes, chili powder, cumin, hot sauce, and salt. Cover, reduce the heat, and simmer until the chicken is tender and no longer pink, the pumpkin is easily pierced with a fork, and the sauce thickens, 10 to 15 minutes. When the chicken is cool enough to handle, shred it and return it to the pan. Stir in the lime juice and cilantro and let the mixture sit while you heat the tacos.