- Preheat oven to 350 degrees. Grease glass baking dish with cooking spray. 
- Chop cauliflower into small chunks. 
- Heat olive oil in large skillet and cook mushrooms, celery, onion and garlic in olive oil for 3-5 minutes. Add bouillon and water, cook and stir until bouillon is dissolved. 
- Combine cauliflower, egg, sage, salt and pepper in bowl. Note: You may need to slightly overseason as cauliflower taste may be overpowering. 
- Mix thoroughly. Stir all ingredients together and transfer to prepared baking dish. Cover with aluminum foil. 
- Bake for 30 minutes. Remove foil and bake for an additional 10-15 minutes.