Preheat oven to 500°.
. Lightly coat both sides of mushroom caps with cooking spray; place mushrooms, gills down, on a foil lined baking sheet. Bake at 500° for 6 minutes; turn caps over, and bake an additional 4 minutes.
. Preheat broiler.
. Bring broth to a boil in a small saucepan; stir in couscous. Remove from heat; cover and let stand 5 minutes. Fluff with a fork; set aside
. Heat 1 tablespoon oil in a large skillet over medium heat. Add garlic; sauté 1 minute. Increase heat to medium-high. Add spinach, 1/4 teaspoon oregano, salt, and pepper; sauté 3 minutes or until spinach wilts. Remove from heat; cover and let stand 2 minutes. Stir in cooked couscous, chickpeas, and feta cheese. Spoon about 1/2 cup mixture into each mushroom cap, pressing gently; top each mushroom with a tomato slice. Broil 6 minutes or until thoroughly heated.
. Combine remaining 1 tablespoon oil, remaining 1/4 teaspoon oregano, and breadcrumbs, and toss well. Sprinkle breadcrumb mixture evenly over tomato slices. Broil 1 minute.