1. Preheat grill to medium-high heat.
2. Combine the first 6 ingredients and 1/8 teaspoon salt in a small bowl.
3. Remove gills from the undersides of mushrooms using a spoon; discard gills. Place mushrooms, onion, and poblano on a grill rack coated with cooking spray, and grill mushrooms and poblano for 5 minutes on each side or until tender. Grill onion 6 minutes on each side or until tender. Remove from heat. Seed poblano and remove stem, and cut mushrooms and poblano into thin strips. Chop onion, and combine vegetables in a bowl.
4. Heat olive oil in a large nonstick skillet over medium-high heat. Add garlic; sauté for 1 minute or until lightly browned. Add mushroom mixture, remaining 3/8 teaspoon salt, and cumin; cook 2 minutes or until thoroughly heated.
5. Heat tortillas according to package directions. Divide mushroom mixture, pico de gallo, and avocado evenly among tortillas. Top each with 2 tablespoons cheese.