Stir together first 4 ingredients in a medium-size microwave-safe bowl. Microwave at HIGH 3 minutes. Stir in rice, and microwave at HIGH 2 minutes.
Stir in 2 3/4 cups broth and 1/4 cup wine. Cover tightly with plastic wrap. (Do not vent). Microwave at HIGH 9 minutes. Carefully swirl bowl without uncovering (to incorporate the mixture), and microwave at HIGH 8 minutes. Carefully remove and discard plastic wrap. Stir in cheese and 1/4 cup chicken broth, stirring 30 seconds to 1 minute or until creamy. Add 1/4 cup additional broth, 1 Tbsp. at a time, if necessary, for desired consistency. Season with salt and pepper to taste.
Meanwhile, sauté portobello mushrooms in hot olive oil in a large nonstick skillet over medium-high heat 6 minutes or until tender. Stir in spinach, and cook 1 minute or until wilted. Stir mushroom mixture into prepared risotto. Serve immediately.
Note: For testing purposes only, we used Rice Select Risotto Italian-Style Rice, an 1,100-watt microwave oven, and a 2 1/2-liter glass bowl. We found that self-sealing plastic wraps, such as GLAD Press'n Seal, do not work in this application.