Trim off ends of zucchini, cook whole in boiling water 10-12 minutes. Drain thoroughly, halve lengthwise and scoop out centers; chip centers and add to spinach. In saucepan blend flour and milk, add spinach mixture. Cook and stir until thick.
Place zucchini halves in shallow baking dish, sprinkle with salt, spoon spinach mixture into shells. Top with cheese and bacon Bake in 350 oven 15-20 minutes.