Preheat oven to 350 degrees. Toss mushrooms with 1 tablespoon olive oil and season with salt, pepper, and sugar. Pour mushroom mixture onto rimmed baking sheet and bake for 20–30 minutes, stirring or turning occasionally until the mushrooms are brown and crispy, but not burnt. Set aside the “bacon” and let cool. Puree avocado, lime juice, and garlic powder in a blender or food processor. Brush ciabatta rolls with remaining olive oil and toast, face down, in skillet or on grill. Assemble sandwiches by first spreading avocado puree, adding tomato slices, and topping with shitake bacon.
Serve with side salad.