First off no, we would not send tanks to the moon. We probably could, but it would be an awful waste. Standard tanks would not operate in the vacuum of space, so we'd need to design new ones from scratch. Trying to keep a soldier with a rifle alive and fighting in that environment would be a nightmare.
Instead, we'll send up a simple guidance computer...and a whole lot of nuclear bombs.
Let's talk rough numbers.
We'll take the US W76 thermonuclear warhead as a baseline. I'm using this weapon because we know the exact weight of the warhead, whereas with other weapons like the W87 details like the weight of the warhead are uncertain.
If we were firing these weapons at a target on the moon, we likely would dispense with most of the reentry casing, since there would be no need to penetrate a thick atmosphere before detonation; that's why we want the weight of the warhead.
A W76 weighs in at 164 kg, and has a yield of 100 kilotons. We'll want to be able to aim these things, so we'll stick a simple solid-fuel rocket onto each warhead - let's round it up to 200 kg per bomb.
The Apollo Command/Service module, the spacecraft that made the full flight too and from the moon, massed around 14,700 kg at launch. The Lunar Excursion Module, the spacecraft that actually landed on the moon, massed 15,200 kg. Call it a combined mass of 30,000 kg going to the moon.
That's the same mass as 150 of our warheads.
Let's say that our strike craft needs around 1,000 kg for a basic guidance computer and storage rack for the bombs. That's still enough mass for 145 warheads. If we manage to build launchers into that mass as well, so we can dispense with the rockets on each bomb, we'd be looking 174 warheads.
Now, to get that kind of mass to the moon, we did need to make use of the Saturn V rocket, which is pretty much the most powerful rocket ever built. If we needed to, we could build new Saturn Vs with a fair amount of lead time - we have all the specs, but the tools and expertise used to build the originals are mostly lost to us, so we'd have to rebuild the industry used to build the rockets. They're probably not our best option.
More likely would be NASA's in-development Space Launch System, or SLS. It's designed to reproduce Apollo-era capabilities with modern hardware, carrying the Orion crew capsule to the moon and beyond. If we wanted to launch a real strike on the moon, this would be the puppy to use.
It's...complicated...to do a clear comparison of two rockets' capacity. The closest comparison would be the 'injected mass' capacity - that is, the mass including upper stages of the rocket itself that can be lifted to a given point. The Saturn V's injected mass capacity was around 154 tons; SLS will manage 173 tons. The two craft are quite comparable, so for simplicity's sake we can assume that the SLS can lift our W76 cluster to the moon.
Without knowing more about the Monster, I couldn't say whether a strike like this would be able to destroy it...but it should at the very least let it know that we're here.