The Champion doesn't know how the Galra spies found this rebel base, and frankly, he doesn't care. He's fresh from his training, given an extra boost of quintessence and ready for his first solo mission. Eliminate the rebels. Destroy the base.

Originally the plan had been to bomb them from orbit, but it's too risky with all the underbrush and trees. It's entirely possible that he'd simply blow the trees out of the way and leave the base untouched, but now very aware they were under attack. If it came to a rebel fleet against one Champion, the odds weren't good, even with his skills, and he wasn't willing to risk that.

Instead, it's an old fashioned stealth mission. The Champion's hair is tied back out of the way, and he keeps to the shadows. If he has to assassinate every single one of these rebels, he'll do it. Their numbers are unknown, which is part of his mission, but the Galra don't anticipate a very large gathering.

He starts from the outside and works his way in, quietly and effectively taking out the rebel patrols and using their keycodes to get inside the building. He has to move fast. No doubt some sort of commander will soon work out that his men are not responding.