Place oil in large skillet and heat over medium heat. Add Chicken and cook, turning as needed, until lightly browned and no longer pink in the center. Remove chicken from skillet and set aside.

Place butter in skillet and melt over medium heat. Add flour and stir until blended in with melted butter. Whisk in milk, broth, ranch mix, salt, and pepper. Bring to a very light simmer while stirring constantly. Reduce heat to low and add frozen vegetables. Cook until veggies are tender, about ten minutes. Return chicken to skillet and stir to combine everything. Serve hot.