Bring a large pot of water to boil. Cook green beans for 6-7 minutes or until tender. Drain well.
Cook onion and mushrooms in butter until tender and onion is translucent, about 5-6 minutes. Stir in flour, salt and pepper. Cook 2 minutes more.
Add milk and cream whisking until thick and bubbly. Remove from heat and stir in soy sauce. Taste and add salt & pepper if needed.
Combine green beans, red pepper, cheddar cheese, and parmesan cheese. Toss with mushroom sauce and place in a 2qt casserole dish.
Combine topping ingredients and set aside.
Bake for 20 minutes. Stir and sprinkle with topping. Bake an additional 10-15 minutes or until bubbly and topping is browned.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)