I bought this exact one at Lidl - very pleasant texture when baked (not at all like spaghetti squash and I am not sure how this would be called "flaky"). Not much fibre, taste sweet and reminiscent of chestnut. The skin is edible (if you must), but tougher than in e.g. Hokkaido squash.
Most winter squash is fairly interchangeable when cooking.
Obviously, there are differences in them (sweetness, density, size, flesh color), but if you're cutting it up and roasting it, then it's fairly universal (but you might need to cut up denser ones into smaller bits).
Tozer Seeds describes it as:
a combination of sweetness, flaky texture and depth of ...
I'll tackle the other part of the question: dealing with high oxalic acid levels (or more precisely: a high oxalic acid : calcium ratio).
I'm aware of two traditional ways of preparing food from high oxalic acid vegetables:
When cooking the vegetables, soluble oxalic acid gets distributed throughout the veggies and the cooking water as well. Throwing away ...
From the photo & description of the leave look & feel, these sound like green wave mustard--a variety of mustard greens with curly leaves.
Mustard greens have a "spicy" or peppery taste, which also seems to align with your experience.
Mustard greens can be safely eaten raw or cooked. It can be a raw salad ingredient, or be sauteed, braised, ...