Freeze friendly baked side dishes No matter how much I love baked food, I cannot avoid a guilty feeling with the environment whenever I turn my oven on. 

Normally I try baking as much as possible in one go to make a better use of the space. Recently I am wondering which type of baked food (ingredients or companions, not full dishes) are OK to freeze and reuse later as a side dish or part of other recipes? 

Although I understand that the flavor will change, I am looking for food that can be baked and still be acceptable later as a side dish itself or part of one.

For example, I was planning baking a batch of bell peppers and see how they test as unfrozen side dish. I also love baked eggplant, but since it is so juicy, the taste loss will be far more dramatic.
Most things baked in a casserole will freeze well ... in part it's because you have a container that's got a relatively low surface to mass ratio, and only exposed to evaporation on one side.

That being said, when you say 'a guilty feeling with the environment', if you're talking about an enviromentalist type perspective, then cooking, freezing, then cooking again is not energy efficient.  (your energy, sure ... but not electricity &amp; gas ... unless it's the trips to the store that you're avoiding).

There are a fair number of cookbooks out there for what's called 'freezer cooking' or 'once a month cooking'.  You  should find a few websites if you search on those terms.  (and we've even had a question about it before).