Components on both sides of the board with reflow
I have seen this done with a two step method.

The most professional way I have been taken part in involved all of the components have a bit of glue sticking them down(technically epoxy). The oven then would heat the top side to the correct temp, then the board was flipped and the board had the top heated. This was being used by a firm that created products exclusively for the military and I believe had strict requirements on reliability and I believe their oven method was very reliable.

I have also seen methods where people use high temp epoxy and then just bake the whole thing at once. You need things lined up carefully because the epoxy will stop things from moving around and normally during reflow parts move into their proper position on the board almost automatically.