Preheat oven to 350. Season chicken breasts with onion powder, paprika, salt and pepper. Place in a baking dish coated with cooking spray. Place artichoke hearts around chicken. In a med skillet, saut mushrooms, green onions, and garlic until tender. Place mushroom mixture on top of chicken. In the same skillet, melt butter and add flour whisking until smooth. Gradually add broth and sherry, cooking until smooth and sauce comes to a boil. Pour over the chicken, cover with foil and bake 45 mins. Remove cover, lift chicken on top of vegetables and continue cooking 15 mins or until chicken is browned and reaches a temp of 155.