Stuffed and baked portobello mushrooms can become soggy. To avoid sogginess:
1. Wipe clean, don’t wash them (they absorb water).
2. Pre-broil to release some of the water.
3. In the final stage of baking or broiling, broil or bake briefly, just until topping is browned. Baking too long will result in mushy mushrooms that have released their liquid into your filling. If that happens, the only thing you can do is to carefully drain the liquid, and place the mushrooms on paper towels to soak as much of the liquid as you can.
Recipe adapted from Healthy Recipes.