Heat olive oil in a small skillet over medium heat. Add onions and cook until lightly brown, about 10 minutes.
While onions are cooking, put the spinach in a large microwave safe bowl and microwave a minute or two at a time until soft. Drain the liquid from the spinach.
In a mixing bowl, combine all ingredients until well blended. Chill for an hour or more. Adjust seasoning before serving.
Notes
If using frozen spinach, partially thaw in the microwave for a few minutes. Drain then continue with the recipe.