Wood will expand and contract across the grain, and a wide panel made of solid wood could change width by a half of an inch, warping the door frame. By allowing the wood panel to float, it can expand and contract without damaging the door.
Put trimmed and cleaned green beans in the steamer basket, set over the boiling water, cover, and steam until tender to the bite, 3 to 5 minutes (depending, again, on how crisp or tender you like your green beans).
Insert the vegetable steamer into the saucepan. Add the cut squash into the vegetable steamer and cover the pot with the lid. Let the squash steam, covered, until crisp tender. This will be about 5-to-77 minutes. Using the pot holder, remove the vegetable steamer from the pot and pour the steamed squash or zucchini into a serving dish. Serve hot with salt and pepper and melted butter if desired.