Preheat your oven to 425F degrees.
Get out a large casserole dish (15x10) and a pie plate for any extras. A couple smaller casserole dishes can work too.
Prepare your vegetables and fruit. Wash the squash. Cut off its ends and cut it in half (NOT lengthwise—cut around the squash's middle.) Using an apple corer remove the seeds from the squash and set aside. Wash, peel, and core your apples. Skin your red onions and cut off their ends.
Prepare your baking dish(es) by greasing lightly with butter or coconut oil.
Mix together the lemon juice, olive oil, cinnamon, butter, and maple syrup and set this dressing aside.
Cut the cored squash, apples, and onions into thin slices (no thicker than ¼ inch).
Now assemble your tian! Starting with a slice of delicata squash add a slice of apple then onion and set it on a plate. Make stacks and stacks of these little squash, apple, onion bundles.
Fan out these bundles (almost like you're playing solitaire with them) and place them in your greased casserole dish. Try to get them somewhat evenly spaced, but it doesn't have to be perfect.
Once you've lined your entire casserole dish with these bundles drizzle the dressing over your tian.
Finally, season with rosemary, marjoram, and black pepper. I don't season with salt at this point—in fact, I usually let my guests season their own food with salt since tastes can really vary. If you do want to add salt, I wouldn’t add more than ½ teaspoon over the entire dish.
Bake in a preheated 425F oven for 15 minutes. If the casserole dish is getting too dry sprinkle with some water, vegetable stock, or apple juice. You want the dish moist not wet.
Bake for another 10-15 minutes or until the edges of the squash, apples, and onions start to brown.
Remove from the oven and let the tian cool for a few minutes before serving. Enjoy!