This is a very easy recipe. Start by preparing the vegetables. Slice the zucchini horizontally into thin strips and the peppers into 4 strips. Heat a tablespoon of olive in a griddle pan, and cook the vegetables on both sides for a few minutes. Put the cooked zucchini and peppers to one side. Next, season the fresh tuna steaks with lots of salt and pepper drizzle with olive oil and quickly sear the tuna in a hot griddle pan for a couple of minutes each side. Meanwhile, as the tuna is cooking, make the lime and avocado mayonnaise by mixing together the mayonnaise, lime juice and zest, and the chopped avocado. You are now ready to start serving. Place the mixed salad leaves in a bowl and drizzle with some balsamic vinegar, olive oil and fresh seasoning. Mix well, and place a handful on your 2 serving plates. Place the slices of grilled zucchini and peppers on top. Finally, place the grilled tuna steaks on top of the peppers (2 pieces per person) and drizzle with the pan juices. Serve the lime and avocado mayonnaise in a small bowl on the side of your serving plates.