In a dutch oven, heat the oil over medium-high heat. Season the chicken thighs generously with salt and pepper and then place them skin side down in the preheated dutch oven. Cook for about 4-5 minutes on each side or until brown. Remove the chicken from the pan and set aside.
Reduce the heat to medium, and add the onion. Cook for 6-7 minutes or until tender. Add the garlic and ginger and cook for an additional 2 minutes. Next, stir in the cumin, coriander, paprika, turmeric and cayenne. Stir to evenly coat the onion. Add the chicken back to the pan, and toss so that the chicken is evenly coated with the mixture. Pour the chicken broth and beer into the pan, submerging the chicken so that 3/4 of the thighs are covered. Bring to a boil, and then lower to a simmer. Cover and cook for 30 minutes.
Remove the chicken, place on a plate and set aside. Increase the heat to medium-high for the sauce. Add the olives and stir in the cornstarch mixed with water. Cook for 10 minutes until the sauce is thickened.
While your sauce is cooking and thickening, cook your couscous per manufacturer's instructions.
Serve the dish by placing the chicken on top of a bed of couscous. Pour sauce over top and garnish with cilantro. Enjoy!