In a small nonstick skillet, heat oil over medium heat. Cook onion and pepper for 3 minutes or until softened. Remove from heat and stir in dill and pepper; set aside.
In a bowl, whisk together eggs and egg whites and milk until combined.
Divide onion and pepper mixture among 6 lightly sprayed muffin tins. Pour and divide in egg mixture among muffin tins. Top each with 2 tomato halves and sprinkle with feta.
Bake in 350° F (180° C) oven for about 20 minutes or until knife inserted in centre comes out clean.
