In a medium saucepan, melt 1 tablespoon butter over medium-high. Add zucchini and saute until crisp-tender, 4 minutes. Stir in orzo and heat until warmed through. Transfer to a bowl and toss with scallion greens; season with salt and pepper.

Melt remaining 1 tablespoon butter in saucepan over medium-high. Add scallion whites and saute until tender, 3 minutes. Add corn and cook until tender, 3 minutes. Add 3 cups water and corncobs and bring to a boil; reduce to a simmer and cook until chowder thickens slightly, about 8 minutes. Discard cobs and season with salt and pepper. In batches, fill a blender halfway with chowder and puree (use caution when blending hot liquids). Serve chowder topped with zucchini mixture.