Yes you can freeze but I'd suggest when defrosting to put in the fridge over night or during the day. Pop into an oven proof dish and reheat until just heated through to avoid over cooking the veg.
Don't put the potato in the dish and serve with mashed potatoes.
Can you do in the crockpot or slowcooker, probably but I've not tried it that way yet.
My non stick stainless steel pot for the stove is oven proof, the dish was taken from stove top to oven.