Preheat oven to 450°F. Place tomatoes, mushrooms and onion in large bowl. Add 3 teaspoons of the olive oil, 1 1/2 teaspoons of the sea salt, thyme, sage and 1/4 teaspoon of the pepper; toss to coat well. In separate small bowl, gently toss avocado with remaining 1 teaspoon olive oil, 1/2 teaspoon sea salt and 1/4 teaspoon pepper.
Place tomato and mushroom mixture on one side of foil-lined shallow baking pan. Place avocado on other side of pan. Roast 35 to 40 minutes or until vegetables are tender and golden brown.
Meanwhile, bring stock and water to boil in small saucepan on medium heat. Cover. Reduce heat to low and keep warm until ready to use.
Carefully add the warm stock mixture and roasted tomatoes, mushrooms and onion into blender container, while keeping the roasted avocados on the baking pan. With center part of blender cover removed to let steam escape, puree on high speed until smooth. (Or puree mixture in saucepan with an immersion blender.)
Pour soup into serving bowls or mugs and top with roasted avocado. Drizzle with additional olive oil just before serving, if desired.