Are commercial pilots incentivized to reduce fuel consumption?
There have been, at various times, and with various carriers, incentive programs set up to encourage pilots to save fuel, improve on-time performance, or some combination of the two.

An example of a fuel-saving incentives program existed at the former Continental Airlines in the early 90s, where pilots would be paid a bonus for using less fuel than planned. The problem was that it wreaked havoc with the schedule itself, as pilots would simply dial back to economy cruise thrust settings, saving fuel but taking noticeably longer to reach their destinations.

An example of an actual-vs-scheduled block incentive program intended to help with on-time performance existed at Silver Airways in their Beech 1900D fleet, whereby pilots would be paid a bonus for each minute they were able to shave off a baseline target time. Ironically enough, it was called the "Green Incentive Program" (don't ask). And it was a can of worms.

I vaguely remember other airlines experimenting with incentives programs relating to fuel consumption and on-time performance, but it's been several years since I left the industry and can't recall any other examples.

In short, yes they do get implemented fairly regularly, but they can be very problematic due to the difficulty in properly designing and managing them (incentivization is a complex problem).

Lastly, since another poster has brought this up, dispatchers do indeed perform most, if not all the flight planning, but the PIC (i.e. Captain of the flight) has the option of overriding most everything the dispatcher plans and arranges for (subject to the carrier's Operational Specifications), including amount of fuel to be carried. Basically, if the Captain decides that the plane is to be filled with as much fuel as it can carry up to MTOW, that's what's going to happen. Might not be the most business-savvy (or even prudent) decision, but it's part of their prerogative as PIC (i.e. the person ultimately responsible for the craft, crew, passengers, and goods onboard).