Preheat oven to 375°.
Combine first 4 ingredients in a small bowl, stirring well with a whisk.
Heat a medium nonstick skillet over medium-high heat. Coat pan with cooking spray. Add ham, bell pepper, and onions; sauté 2 minutes. Stir in egg mixture. Reduce heat to medium, and cook 5 minutes, stirring occasionally for first 2 minutes. Top mixture with cheese. Wrap handle of pan with foil; bake at 375° for 12 minutes or until center is set. Cut frittata into 4 wedges.