In a small bowl, toss the avocado with the lemon juice, season with salt and pepper, and set aside.
In a medium bowl, whisk together eggs, egg whites, milk, rosemary, salt, and pepper.
In a nonstick skillet, heat 1 tablespoon oil over medium. Add onion and cook until tender, about 4 minutes. Add jalapeno and spinach; cook until the spinach has wilted, about 1 minute. Transfer to a bowl; stir in chives and cheese; set aside.
Wipe the skillet and add 1 tablespoon oil. Add half the egg mixture and cook until nearly set, 1 to 2 minutes. Spoon half of the spinach mixture into the center, fold the omelet over, halve crosswise, and place on serving plate. Top with half the avocado. Repeat with remaining tablespoon of oil, egg and spinach mixtures, and avocado. Serve with mango and kiwi.