I don't know where this recipe originated, it's kind of just always been there. My mother made this every year when I was growing up, and I hated it as a kid. As I got older I would help make the kugel, first by cutting vegetables, then sauteeing the faster vegetables, and then making the entire thing.
It's a big job, so schedule the time for all of these vegetables! But it's also delicious, and super worth it if you like vegetables. This is (as noted above) a recipe where kids can be a huge help.
Prep time - get organized. Start with the eggplants so they're boiling as you're cutting everything else. I usually am also boiling eggs and potatoes while sauteeing because I'm at stove anyhow. Figure one person doing it along should devote at least 90 minutes to cutting and sauteeing
1 large eggplant, peeled, cubed
2-3 onions, cubed
1 each red and green pepper, diced
3 stalks celery, sliced
2 zucchini, cubed
1 cup mushrooms, diced
½ stick butter
½ lb. mixed cheeses
½ cup matzah meal (gluten) or potato starch (gluten-free)
Boil the eggplant for 10 minutes, drain well, and mash. Sautee all other vegetables.
Mix all ingredients together, reserving some cheese and matzah meal for topping
Bake in a 9x13 pan uncovered at 350 for an hour or so
I often double the recipe so I don't have to do all the work twice. Just separate the items between two tins as you prep them, then mix them each and bake them side by side in the oven.
If making this gluten-free, the potato starch for the matza meal is a great substitute. The flavor here comes from the vegetables.