Basically what the title says. How do I place Item Frames in world gen? I can make a dozen or so blocks to get around the issue,  but I'd rather just place Item Frame entities on the wall. Is there a way to do this?

As the Item Frame is an Entity you cant place it in the World by worldgen easily but it is still accessible in Item Form with the ItemHangingEntity.class so you should be able to place one of them in the World with the given parameters.

new EntityItemFrame(world, x, y, z, direction)

Oh, so you have to place it from the Entity side, cool, thanks.  While I have you here, is there an accessor method in the Entity class for placing items in the frame? I can check when I get back to my computer, but are there any tricks I should know there?

Yeah

there is a setDisplayedItem function in the Entity Class. I guess that should place an Item in there.

EntityItemFrame frame = new EntityItemFrame(world, x, y, z, direction);
frame.setDisplayedItem(ITEMSTACK TO DISPLAY);

Should do what you want.

Perfect! You've been more than helpful

And then after these two lines a call to

world.spawnEntityInWorld(frame);