This is perfect for backyard grilling, or campfire grilling. I prepare packets like this when we go camping, and store the foil packet inside a sealed ziploc bag in the ice chest till i'm ready to cook it. This is by far my family's favorite side dish when we cook outside at home or while camping.
Start by making a fairly large packet out of heavy duty foil. Make sure you seal up the sides well so the butter wont leak out.
slice or cube up the 1/2 stick of butter and spread the pieces throughout the inside of the foil packet.
slice your freshly picked summer squash into 1/8" or thinner slices. the best squash for this recipe is yellow crookneck or any small sized summer squash like zucchini. spread slices evenly throughout foil packet.
thinly slice 1/2 a purple onion, add to packet along with fresh garden basil (about 5 to 7 leaves, i use the blooms pulled off the stem too), chopped fresh garden chives, thinly sliced red bell pepper (optional- some people can't digest these), and then sprinkle in white pepper, sea salt or garlic salt to taste.
seal up the 3rd edge on your foil packet and lay flat on the grill -- indirect heat (do not cook directly over the flame). cook each side of the packet for about 20 minutes, depending on how many squash you have in there the cooking time will vary.