Heat olive oil in a large skillet over medium heat. Add garlic and cook for 10 seconds. Stir in mushrooms and season with salt; cook until soft, about 8 minutes. Remove from heat.
Place mushrooms in a large bowl and add tomatoes, carrots, onion, cilantro, serrano pepper, and jalapeno pepper.
Combine lime juice, tomato juice, ketchup, and pickle juice in a second bowl. Pour over mushroom mixture and let stand for 20 minutes. Serve garnished with avocado slices.
