Cut zucchini diagonally into 1 cm thick slices. Mix them in a bowl with 3 tablespoons olive oil and rosemary.
Drain tuna and place in a small mixing bowl. Add mayonnäse and 2 tbsp. olive oil and puree all. Season with salt and pepper and a little lemon juice.
Preheat the oven to 160 °. Season chicken breasts with salt and pepper and fry them in an ovenproof roasting pan on both sides 3 minutes each. Then fry them for about 10 minutes in the oven on the middle rack. Grilling zucchini slices on both sides briefly or roast and season with salt and pepper. Keep vegetables warm.
Cover the plates with the tuna sauce. Cut chicken breasts into slices and arrange on the plates. Add zucchini and capers. Sprinkle with pepper and basil.