Whisk the balsamic sauce ingredients together in a medium bowl. Remove 2 tablespoons and add to a bowl or freezer bag with the chopped chicken; set aside to marinate while you chop the veggies and steam the sweet potatoes (up to 30 minutes at room temp or 4 hours in the fridge). Reserve remaining sauce for later.
Add chopped sweet potatoes to a microwave safe bowl with a lid. Add water it reaches ¼-inch up the sides. Cover and microwave for 5-7 minutes or until fork tender; drain and set aside.
Melt butter in olive oil in a large skillet over medium-high heat. Sauté chicken for 1 minute then add shallot and cook just until the outside of the chicken is no longer pink. Add the asparagus, and tomatoes and cook an additional 1-2 minutes or until asparagus are crisp-tender. Add garlic and sauté 30 seconds.
Add the sweet potatoes back to the skillet along with the remaining balsamic sauce (that didn’t touch the raw chicken). Cook, stirring constantly, until chicken is cooked through and the sauce is thickened, about 1 minute. Taste and add brown sugar for sweeter, balsamic or lemon juice for tangier. Dig in!
