Heal Evoker Staff GW2 Evoker WvW Builds
Evoker picks a favourite element. 
Evocation has you choose one, cuts that attunement's recharge and gives you a familiar of it. The familiar's basic skill charges as you cast, faster when you cast in its element, and three uses unlock its empowered skill. The line also hands you meditations.
Our heal Evoker takes that to its conclusion with 
Specialized Elements, which locks you into the element you chose and refunds weapon recharge for using familiar skills instead of swapping. The healing then lives on meditations and the familiar rather than on a channel, which is the whole argument for it: Heal Tempest has to stand still to overload and this does not. 
Altruistic Aspect turns all three of its meditations into boons for the group.
The power Evoker keeps its attunements and builds around burning. 
Burning Precision makes your critical hits burn, and 
Fiery Might, 
Pyromancer's Training and 
Persisting Flames all pay strike damage for burning targets. 
Galvanic Enchantment folds the familiar into the same loop: after a familiar skill your next strikes arc chain lightning, and evoker chain lightning burns.
2 Evoker builds
Heal Evoker Staff Power Evoker Spear Playing Evoker in WvW
The familiar is a second set of cooldowns that you charge by playing normally, and both builds feed it. 
Familiar's Prowess gives you a bonus after every familiar skill and 
Familiar's Focus improves it; on the heal build, Specialized Elements makes those same skills refund your weapon recharge on top.
What you give up is elemental flexibility. Specialized Elements is not a figure of speech — you cannot leave your selected attunement — so the heal build has one element's weapon skills for the entire fight and no 
Rock Solid 
Stability to hand anyone. The power build keeps all four attunements, but its damage is priced in burning, so a target that cleanses is a target you hurt less.
Evoker is the newest of these specs and the builds show it: they are honest, uncomplicated packages with no tricks in them. If you want the support with the longer record in a zerg, Tempest has been doing that job for years.