Season the chicken breast lightly with salt and pepper, then grill over medium heat until fully cooked, about 5-6 minutes per side. Once cooked, dice into small bite-sized pieces.
In a medium saucepan, warm the vegetable broth and keep it on a low simmer.
In a separate large pan, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 2-3 minutes.
Add the minced garlic and sliced mushrooms to the pan, cooking until the mushrooms are tender and start to brown, approximately 4-5 minutes.
Stir in the Arborio rice, ensuring each grain is coated in the oil and vegetables. Toast the rice for about 1-2 minutes.
Begin adding the warm broth gradually, one ladle at a time, stirring constantly. Allow the rice to absorb the liquid before adding the next ladle. Continue this process until the rice reaches a creamy consistency and is fully cooked, about 18-20 minutes.
Fold in the diced grilled chicken and grated Parmesan cheese. Stir until the cheese melts into the risotto, adding extra broth if needed for a creamier texture.
Taste and adjust seasoning with salt and pepper as needed. Serve warm and enjoy your healthy, creamy mushroom risotto.