Place 1 in. of water in a large saucepan; add cauliflower. Bring to a boil. Reduce heat; cover and cook for 6-8 minutes or until crisp-tender. Drain and pat dry.

Meanwhile, in a large saucepan, saute green pepper and mushrooms in butter for 2 minutes or until crisp-tender. Add flour; gradually stir in milk. Bring to a boil; cook and stir for 2 minutes or until thickened. Remove from the heat; stir in cheese until melted. Add pimientos and salt.