In a large stockpot over medium heat, cook the ground beef until just beginning to brown. Season lightly with salt and black pepper.
Add onion and mushrooms.
Stir in the chopped onion and sliced mushrooms. Cook until the onions become translucent and the mushrooms have softened.
Incorporate remaining ingredients.
Add the green bell pepper, diced celery, uncooked rice, orzo, bouillon cube, onion powder, and water. Stir well to combine.
Bring to a boil.
Increase the heat and allow the mixture to come to a full boil. Cook for 2 minutes.
Simmer.
Reduce the heat to low, cover, and simmer for 35–45 minutes, or until the rice is tender and the dish is moist. If the mixture becomes too dry during cooking, add 1/4 cup of water at a time until the desired consistency is achieved.
Adjust seasoning and serve.
Taste and adjust with additional salt and pepper as needed. Serve hot.
Notes
To make this recipe gluten-free, substitute the orzo or vermicelli with certified gluten-free pasta or an additional 1/4 cup of rice. Confirm that the bouillon cube used is gluten-free, as some brands may contain wheat derivatives.