In a large skillet over medium-high heat, add the oil. Saute the union and bell pepper for 3 to 5 minutes, or until softened. Add the turkey and saute for 5 to 8 minutes, or until the turkey is cooked through and any excess liquid has evaporated. Add the garlic, chili powder, and cumin and saute for 1 minute. Add the tomato sauce and chipotle, reduce the heat, and simmer, stirring to combine. Cook for 5 minutes, stirring occasionally. Add the beans and cook for 2 to 3 minutes, or until heated through. Season with salt and pepper.
Meanwhile, wrap the tortillas in aluminum foil and bake for 10 minutes.
In a bowl, coarsely mash the avocado and stir gently with lemon juice. Season with salt.
Spoon the turkey mixture onto the tortillas and top with a dollop of avocado.