Season the chicken breasts generously with salt and pepper. Heat a large skillet over medium-high heat, then add olive oil until shimmering. Place the chicken in the pan and cook for 5-7 minutes on each side until golden brown and cooked through, then transfer to a plate to rest.
In the same skillet, add minced garlic and cook for about 30 seconds until fragrant, stirring constantly to avoid burning. Then, stir in chopped sun-dried tomatoes and cook for another minute, allowing their smoky sweetness to infuse the oil.
Pour in the heavy cream, scraping up any browned bits from the bottom of the pan. Stir in grated Parmesan cheese if using, and bring the mixture to a gentle simmer. Cook for 3-4 minutes until the sauce begins to thicken slightly and coats the back of a spoon.
Return the cooked chicken breasts to the skillet, spooning sauce over them. Add chopped greens on top, cover the skillet, and cook for another 3-4 minutes until the greens are wilted and chicken is heated through.
Finish by stirring in lemon juice and adjusting seasoning with salt and pepper. The sauce should be creamy, glossy, and clinging to the chicken and greens. Let it rest for a couple of minutes, then serve hot, spooning extra sauce over each plate.
