In a large nonstick skillet, heat olive oil over medium heat. Add onion. Cover and cook in hot oil for 10 minutes, stirring occasionally. Uncover and add mushrooms. Cook, uncovered, for 8 to 10 minutes or until mushrooms are tender and onion is golden brown, stirring occasionally.
Add cream cheese, blue cheese, milk, thyme, salt, and pepper to onion mixture. Cook and stir over low heat until mixture is melted. Serve warm with pear slices, melba toast, and/or whole grain crackers.