Roast garlic dressing:
Preheat oven to 180°C. To prepare the dressing, place garlic on a baking tray and roast in preheated oven for 30-35 minutes or until the garlic cloves are soft. Remove from the oven and set aside for 10 minutes to cool slightly.
Cut tops off garlic bulbs, squeeze soft garlic from each bulb, and place in a blender. Add red wine vinegar and season with salt and pepper. Blend until well combined. With motor running, gradually add oil in a thin steady steam until mixture is thick. Gradually add enough hot water to make a pouring consistency.
Salad: Place the tatsoi, spinach and avocado in a large serving bowl and toss gently to combine. Drizzle the dressing over the salad.