(adapted from Flavor Your Life's Balsamic and Mustard Chicken Thigh Casserole)
Drizzle 3 tablespoons of olive oil in bottom of slow cooker. Lay boneless, skinless chicken breast on top of oil.
Dice carrots, mushrooms, bell peppers and zucchini and toss veggies on top of chicken in slow cooker.
In a small bowl, whisk together tomato sauce, dijon mustard, brown mustard, balsamic vinegar and brown sugar. Pour over chicken and veggies.
Cook on low for 4 hours or until chicken is cooked through and tender.
Gently stir chicken and veggies together. Spoon servings onto plate. Give each plate a quick drizzle of olive oil before serving.