Place tuna in a shallow bowl. Whisk together oil, balsamic vinegar and chilli, pour over tuna and season.
Heat a pan and sear tuna on each side until browned and cooked to your liking. Set aside and keep warm. Reserve the pan juices.
For the mayonnaise, place garlic, egg yolks and wine vinegar in a blender, blitz for 30 seconds, then slowly add oil in a steady stream until the mixture is thickened and creamy. Stir through lemon juice and capers, and season. Thin with a little warm water if required.
For the salad, toss together all the ingredients, drizzle with olive oil and season.
To serve, place tuna on a platter, pour over pan juices and slice. Garnish with micro herbs and serve with the caper mayonnaise and salad on the side.