I've read in a few Watchman guides that in the opening rotation, you should go Force Melt -> Zen. I don't understand why though; given that Zen increases the crit chance of all your burn attacks, shouldn't you do Zen -> Force Melt? What am I missing? Thanks.

Zen only buffs your next 6 dots, considering that your hardest hitting dot is Overload Saber (with three stacks), you'll want to maximise the amount of those dot ticks to get buffed by Zen. Because the GCD after Force Melt you'll be applying your third stack (at least if you're following Oofalong's rotation), that's when you want to hit Zen (before you actually apply the third stack, since it ticks on impact). Edited October 6, 2018 by AdjeYo

To add to what Adjeyo says, Force Melt is not a saber attack, so it does not apply the 3rd stack of Overload Saber. It's important to delay the 3rd stack of Overload Saber because each time you apply a stack, it refreshes Overload Saber. Thus Zen after Force Melt and right before your next melee attack. Edited October 8, 2018 by Rion_Starkiller