Preheat the oven to 400 degrees.
Cut the ends off each squash, then slice lengthwise and use a spoon to remove the seeds. Cut into 1/8-inch thick crescent moons.
Cut the onion in half, then slice into thin half-rounds.
Put the coconut oil into a small saucepan over low heat until melted.
In a large mixing bowl, toss the squash, onion, coconut oil, cumin seed, mustard seed, rosemary, and salt.
Spread the mixture out into an even layer on one or two parchment-covered sheet pans.
Bake for 15 minutes.
Rotate the pans 180 degrees and bake for another 10 minutes, or until the squash turns fork-tender and golden brown.
Remove from heat. Put the squash back into the mixing bowl and toss with olive oil, vinegar, nuts or seeds, and fresh chopped herbs.