Heat oil in large skillet on medium-high heat. Add mushrooms; cook 4 min., stirring after 2 min. Add garlic; cook 1 min. or until garlic is fragrant and mushrooms are tender and browned, stirring frequently. Stir in pasta sauce; simmer on medium heat 5 min. or until heated through, stirring frequently. Remove from heat. Add spinach; stir until spinach is wilted and evenly coated with sauce.