Hi, Dancing Girl.
I eat zucchini. I don't peel them. I can eat the peels now, but I didn't when I came home from surgery, too risky at that early stage. Now, I slice and toss with olive oil, salt and pepper, and and roast in the oven until soft. Theyncook really fast so don't leave them for long. I think olive oil or avocado oils help to "lubricate" your insides and it's good for you. The gel consistency of cooked zucchini helps give substance to stools, as you say, it "plumps" up.
I make my own potato salad and eat this in moderation and it works excellently. Spaghetti or linguini also gives me good results. I do not need any bulking agent or medication related to my j pouch, and haven't for three years. I eat lots of steamed or broiled fish and this makes soft, easy results. I think any vegetable, as long as it is roasted or cooked to a soft consistency, and chewed very well, will help with formation and solidify things without making cement. I eat everything, including mushrooms and Brussels sprouts, raspberries, strawberries, but I never eat nuts or seeds because they don't break down. I eat plainly, meaning broiled, roasted, baked, boiled foods, and no cream-based sauces or heavy gravies that are made with flour (carbs = messy pouch results).
When I buy prepared food, I read the label: if I recognize and can pronounce the first five ingredients, and if it isn't full of overly processed sugar, starches, fillers, and carbs, I will buy it. The only supplement I take is 1,000mg tablet of vitamin D, and my diabetes medication, low doses. That's it. I am healthy, and no pouch issues.