The fight can be broken into 4 steps:
Before pulling General Vezax assign casters to groups to rotate through the process of regenerating mana through the clouds.
Pull General Vezax, and start DPSing.
Interrupt Searing Flames when General Vezax starts casting it.
When General Vezax casts Surge of darkness stop all DPS on him. Have the tank kite him, since General Vezax will move 55% slower. It should be the perfect time for your casters to start taking the clouds for mana regeneration, and the healers to start AOE healing them.
Rotate through the caster groups to not overwhelm your healers.