Combine parsley, thyme, rosemary, and garlic. Set aside.
Heat oil in a large nonstick skillet over medium-high heat. Add mushrooms, leek, 1/4 teaspoon salt, and 1/8 teaspoon black pepper; sauté 10 minutes or until liquid evaporates and mushrooms are lightly browned. Add half of parsley mixture; cook 1 minute, stirring constantly. Stir in bell peppers. Remove from heat; cool slightly.
Combine remaining 1/4 teaspoon salt, remaining 1/8 teaspoon black pepper, remaining parsley mixture, milk, egg substitute, and 3/4 cup cheese in a large bowl, stirring with a whisk. Stir in mushroom mixture. Add bread; stir gently to combine. Let stand 10 minutes. Spoon into a 2-quart baking dish coated with cooking spray. Sprinkle with remaining 1/2 cup cheese. Bake at 350° for 45 minutes or until pudding is set and lightly browned.