1. Pat the chicken cubes dry with paper towels. Season them generously with salt and black pepper. This step is crucial for developing flavor and ensuring a nice sear.

2. Heat the olive oil in a large skillet over medium-high heat. Add the seasoned chicken in a single layer, working in batches if necessary to avoid crowding the pan. Cook for 3-4 minutes per side, until golden brown and cooked through. Remove the chicken from the skillet and set aside on a plate.

3. Reduce the heat to medium. Add the thinly sliced onion to the same skillet. Cook, stirring occasionally, for 5-7 minutes until the onions are softened and translucent. Pour in the balsamic vinegar and sprinkle in the granulated sugar. Continue to cook for another 3-5 minutes, stirring frequently, until the onions are deeply caramelized and the liquid has reduced to a sticky glaze.

4. Pour the chicken broth into the skillet, scraping up any browned bits from the bottom of the pan with a wooden spoon. Bring the broth to a simmer and let it cook for 2-3 minutes, allowing it to reduce slightly.

5. Stir in the heavy cream and thawed frozen peas. Return the cooked chicken to the skillet. Let the mixture simmer gently for 3-5 minutes, allowing the sauce to thicken slightly and the flavors to meld. The sauce should coat the back of a spoon.

6. Remove the skillet from the heat. Stir in the grated Parmesan cheese until it’s fully melted and incorporated into the sauce. Taste and adjust seasoning with more salt and pepper if needed. Garnish generously with fresh chopped parsley before serving.