To make the pesto, blitz all the ingredients with a steady stream of extra-virgin olive oil to make a smooth and creamy pesto. Store in a clean glass jar in the fridge for upto a week.
Heat 2 tablespoons of olive oil in a deep casserole dish or Dutch oven. Put in the chicken thighs and sear to brown on both sides for about 3-4 minutes. Set aside.
Heat the remaining olive oil on medium heat and sauté the onions. When the onions are translucent, add the garlic and cook for a further 30 seconds followed by the pesto.
Cook for 3 minutes, then pour in the red wine and the water. Bring up to a boil and put in the chicken. Season with salt, reduce to a simmer, cover and cook for 20-25 minutes on slow till the chicken is cooked through and the sauce is reduced.
Toss in the red grapes, add the pepper, cook for a minute and serve. Alternatively, cool, replace the lid and refrigerate till needed.