The problem with reheating grilled vegetables like that , with chopped onion, is that the grilled onion parts get grilled again, and they get burned a bit.
Yes, I love them really on the border of burned, dark brownis with some black lines. So I bake them the first time that way. Reheating burns then just a bit to far then. Stll giving a good smell and taste to the rest of the vegs