Preheat oven to 325 degrees F. Liberally coat a 12-cup muffin tin with cooking spray.
Heat oil in a large skillet over medium heat. Add broccoli, bell pepper, scallions and 1/8 teaspoon salt; cook, stirring, until the vegetables are tender, about 5 minutes. Remove from heat and let cool for 5 minutes.
Whisk eggs, Parmesan, milk, pepper and the remaining 1/8 teaspoon salt in a large bowl. Add the vegetable mixture and stir to combine. Divide the egg mixture among the prepared muffin cups. Bake until firm to the touch, 25 to 28 minutes. Let stand for 5 minutes before removing from the tin.
To make ahead: Refrigerate egg mixture overnight. Let stand at room temperature for 10 minutes before baking.
1 1/2 medium-fat protein, 1 fat, 1/2 high-fat protein, 1/2 vegetable