Melt the butter in a large skillet over medium high heat.
Add the onions, cooking until softened and starting to brown.
Sprinkle with salt, pepper, garam marsala, turmeric, ginger, smoked paprika, garlic powder and cayenne, stir to combine.
Add the chicken, cooking until browned (does not need to be cooked through at this point).
Stir in the beer, scraping to deglaze the bottom of the pan.
Stir in the tomato paste, then the Greek yogurt. Lower heat, simmer until the chicken is cooked through, about 5 minutes.
Serve over rice, sprinkle with parsley.