Heat a skillet over medium heat and add the olive oil and butter. Saute the onions and garlic until they start to soften. Add the cumin, tomatillos, and peppers to the pan and saute for a couple of minutes.
Stir in the flour, and cook for a minute more, stirring. Then add the chicken stock and lime juice and continue to stir well while it comes to a simmer.
At this point you can transfer to a slow cooker if you like. Or continue on the stove.
Add the turkey, beans and oregano and simmer very gently until the peppers are tender. This should only take about 10 minutes or so. Add salt and pepper to taste, and then stir in the heavy cream. Bring up to a simmer again and taste the soup to see if you need to adjust the seasoning.
If using the slow cooker, put everything in except the cream. Cook on low for up to four hours, and then stir in the cream and heat through.