Pat the chicken pieces dry with paper towels, then season on all sides with Kosher salt and black pepper.
Heat olive oil in a large skillet over medium-high heat. When hot, and working in batches, add the chicken pieces and cook. Rotate the chicken every few minutes so that it’s evenly browned. Transfer the chicken to a plate.
To the same pot, add chopped onion, sliced mushrooms, diced red and yellow bell peppers, and diced pancetta. Cook, stirring often. Season with remaining Kosher salt, then add chopped garlic, fresh sage leaves and rosemary sprigs. Cook.
Pour in dry white or red wine, then bring to a boil. Allow the mixture to reduce by half. You can either break them up with your hand as you add them to the pot or use a spatula. Add a pinch of sugar, then return the chicken, along with any juices on the plate, to the pot.
Once the chicken is fully cooked and the sauce has reduced substantially, remove the lid. Stir in black olives, then taste the sauce and adjust seasoning. Transfer to a serving platter, then garnish with fresh basil and a pinch of flaky sea salt. Enjoy!