Squash is good roasted with garlic and maybe thyme. You could also steam or boil it most of the way through and top it with toasted pumpkin seeds, since it's autumn. Or, if he approves of the texture, you could roast it through and then puree it with garlic and parmesean cheese - it'll make a thick yet chunky side with a tang from the cheese. Also, I think all veggies like that are great grilled with just a little olive oil on top. You could top it with a fresh pesto, which is just toasted pine nuts (or any nut you like) pureed with fresh basil, garlic and olive oil.