Preheat oven to 400. Butter a 2 qt casserole dish or 9x13 baking pan. Gently steam the green beans just until tender, but still firm. Arrange in bottom of pan.
Melt 4 tablespoons of butter over medium-low heat, add onions and saute until translucent. Add garlic and saute until fragrant. Whisk in flour and cook for 2-3 minutes, whisk in milk, bring to a simmer, stir in red peppers and cheese. Turn off heat and stir until cheese is melted. Season with salt & pepper to taste.
Pour the sauce over top of green beans. Combine the crushed crackers, remaining 4 tablespoons melted butter and parmeasan cheese and spread over top of casserole. Bake 20-25 minutes or until golden brown.
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