Step 2

Preheat oven to 325°F. Liberally coat a 12-cup muffin pan with cooking spray.

Step 3

Heat oil in a large skillet over medium. Add onion and 1/8 teaspoon salt; cook, stirring, until starting to soften, about 3 minutes. Add bell pepper and oregano; cook, stirring, until vegetables are tender and starting to brown, 4 to 5 minutes. Remove from heat and let cool 5 minutes.

Step 4

Whisk eggs, feta, milk, pepper, and remaining 1/8 teaspoon salt in a large bowl. Stir in spinach, olives, and vegetable mixture. Spoon mixture evenly into prepared muffin cups. Bake at 325°F until firm to the touch, about 25 minutes. Let stand in pan 5 minutes before removing omelets.