Beat cream cheese in a large bowl at medium speed of an electric mixer until creamy. Add milk, egg substitute, and pepper; beat until smooth. Stir in cheese.
Coat a large nonstick skillet with cooking spray; place over medium heat until hot. Cook spinach and next 3 ingredients just until tender and liquid evaporates. Cool slightly.
Combine egg mixture and spinach mixture, stirring well. Pour into a 10-inch quiche dish coated with cooking spray. Bake, uncovered, at 350° for 45 to 50 minutes or until center is set. Remove from oven and cool on a wire rack 10 minutes.
Cut into 8 pieces, and serve with salsa, if desired.