I feel the exact same way about my lunch, i want high volume, low calorie, high protein, little prep food.
i usually eat greek yogurt. specifically without sugar or artifical ingredients. pretty high protein %, great gut bacteria. you can even add some nuts to it. the prep can range from pretty much nothing to adding and combining lots of stuff.
I usually eat fage 2% yogurt, and its about 50-55grams of protein per 300 calories.
High protein tortilla wrap, preferably wholemeal, a tablespoon of hummus (low fat if you wish), pre cooked chicken breast or quorn fillet (seasoned if you wish), low fat mozzarella, sliced red peppers and cherry tomatoes.
Just made one and from the packets I used, here are the aggregates: Protein: 54g, Calories: 401, Carbs: 44g, Fat: 22g, Sats: 2.1, Sodium 0.9g.