Place the sliced carrots in a large skillet or saucepan. Add enough water to cover them by about 1 inch. Bring to a boil over high heat and cook until the carrots are tender-crisp, about 5 minutes (timing depends on thickness). They will cook a bit more in the next step, so drain them as soon as they are nearly done. Pour off the water and return the carrots to the pan.

Add the butter, brown sugar, lemon juice, and cinnamon to the pan with the carrots. Cook over medium heat (reduce to medium-low if the mixture bubbles too vigorously) for about 5 minutes, stirring occasionally, until the sauce thickens slightly and the carrots are cooked to your liking.

Season with salt and pepper to taste. Serve immediately, garnished with chopped parsley if desired.