Rinse and dry your squash and zucchini. Trim off the ends and discard then slice into ¼ to ½ inch thick rounds.
Pile the veggies in the center of a sheet of tin foil that is around twice as long as your pile. Mine was around 18-20 inches long. Season with salt and pepper then scatter the chunks of butter over top.
Bring the long sides of the foil together and fold the last inch of the edges over each other to seal them together. I usually crinkle the fold to help it hold better.
Then fold the edges up on each end until you get just about to the veggies inside. You want the pouch snug, but not too tight.
Heat your grill to medium-high heat and place the foil pack directly over the heat.
Cook for around 8 minutes, flipping occasionally. For softer veggies cook for 10-12 minutes.
Transfer the foil pouch to a plate and carefully open the pouch. There will be a lot of hot steam when you open the pouch, so it's best to cut it open with a knife or use a towel to protect your hands.