Preheat oven to 350°F. Heat oil in large nonstick skillet on medium-high heat. Add onion; cook and stir 5 minutes or until tender. Add spinach in 2 batches; cook and stir until almost wilted.
Mix remaining ingredients in large bowl until well blended. Add spinach mixture; mix well. Spoon into 2-quart baking dish.
Bake 20 to 25 minutes or until heated through and edges are bubbly. Let stand 1 minute; stir. Serve with vegetable dippers and assorted crackers or sliced French bread.