Orzo and Chicken Stuffed Peppers

Preheat the oven to 375 degrees F (190 degrees C). Spray inside of green, red, and yellow bell pepper halves with cooking spray; place on a baking sheet. Bake peppers in the preheated oven until slightly tender, about 10 minutes. Heat 1 tablespoon butter and 2 tablespoons oil in a skillet over medium heat; cook and stir 3 green onions and garlic until fragrant, 2 to 3 minutes. Add chicken, black pepper, and cumin; cook until chicken is no longer pink in the center and juices run clear, 4 to 5 minutes. Add orzo and chicken broth; simmer until orzo is cooked through but firm to the bite and broth is absorbed, about 11 minutes. Spoon chicken-orzo mixture into the bell peppers; sprinkle with Parmesan cheese. Bake in the preheated oven until cheese is melted, about 7 minutes. Heat 1 teaspoon oil and 1 teaspoon butter in skillet; Cook and stir portobello mushrooms and remaining green onion until tender, about 5 minutes. Season with salt and black pepper. Spoon about 2 tablespoons mushroom mixture onto each stuffed bell pepper.