The level design in Prosper Bluff often features choke points where Secret Skills like Bellow can be highly effective. Use your skills strategically, remembering their cooldowns. You'll find another Shard at the end of this level, guarded by a more substantial group of enemies, possibly including a few shielded Squirts and Gasfellas.
Clear the area, grab the Shard, and return to the Bastion. With this Shard, you'll be able to restore another structure, perhaps the Lost-and-Found, which allows you to purchase items you might have missed or additional Secret Skills. Always check the Bastion after each mission for new opportunities.