Bioluminescence, refined, could lead to the evolution of lasers. But is it worth the implications?
1) Creating a powerful beam within the electromagnetic spectrum requires energy.
Any organism with a laser will have to eat nutritious food, constantly, to meet the energy requirements of such an organ. The exact amount of energy required depends on the size of the laser and the organism that wields it. When an organism finally does eat enough to maintain a laser, however, our next problem arises:
2) If an organism has excess energy, it will use it practically.
Unless a laser is exactly what your creature needs, it will use the energy it gets to maintain existing systems, or it will evolve a more efficient, more reasonable way of defending itself, and channel energy to that organ instead. Why would humans evolve lasers that aren't likely to do much damage when they could instead evolve sharper teeth, or spit acid?
Assuming an organism meets the energy requirement, how can a practical laser evolve?
An organism with prexisting bioluminescence, such a firefly, that controls when it releases light, is an ideal candidate to evolve a laser-bearing species from. However, fireflies use their lights to find mates and communicate, which lasers will not help them with. Then what is a practical use of a laser that a creature would want to evolve?
Going on the offensive is not practical. A laser will not evolve if a firefly tries to kill its enemies with blinking lights. You will only end up with lots of dead fireflies.
Using lights for defense? Why not. If blinking lights stun or confuse predators, and your creatures become dependent on this as a species, then the individuals with the most effective, concentrated, and blinding lights will survive to reproduce or be favorited by mates. Over time, this could lead to extremely concentrated beams of light similar to lasers. Not exactly a traditional laser, but technically, it still is one. After your lasers are concentrated, your organisms may discover that they can do damage with them, too. It depends on how concentrated, and I don't have the math or means to say.
Two additional things to note:
A) You want a land creature, but I used fireflies as an example. No problem! As long as your land creature has evolved bioluminescence, my steps to evolving lasers should still work.
B) Wouldn't heat and self-damage cause problems? Nope, and here's why: bioluminescence is efficent. Fireflies do not heat up when they shine their lights because their process is extremely productive. This could go for your organism as well. Finally, self-damage would only occur if the lasers evolved to be extremely powerful. At this rate, a large organ shaped like a dish, that concentrated all beams in one direction, would likely stop any tissue from taking too much of the radiation.