I am reworking The Lost Mine of Phandelver from the Starter Set by giving it a Wild West / Spaghetti Western / Zorro-esque spin to it and calling it...
Chuck Dagger, human rogue
Marshal Heeling, human cleric
Vanciana Feyzalez, elf wizard
Mucho Cerveza, dwarf fighter
Act I, Scene 1: Las Flechas Del Duende
(Map made using tools available in Roll20. Here is a screen shot sans grid, tokens, and labels.)
Featuring the Duende ("Greenjuns," pejoratively): Festering Wound, Running Wart, Oozing Boil, Pulsing Pimple - goblins, as per Starter Set. Their motivation is to steal the crowbars, miner's picks, and shovels, kill the oxen, and burn the wagon, then escape up the Duende Trail. (Goblins have 23 lbs. of gear including a tinderbox each, so they can carry another 97 lbs.) If the duende can make it off the map through the spot marked "Duende Trail," they are considered to have escaped with whatever goods they were carrying so the PCs will have to deal with them in a future scene. The duende will only spend actions attacking if they have no other options such as if the PCs are completely blocking their ability to steal from the wagon. In all other cases, they pursue their motivation unto death.
Don't forget their bonus action to Disengage and Hide - this will likely provide quite useful in pilfering from the PCs. They can also force the oxen to move into a better position by attacking them. The dry brush will be a great advantage to the duende as well. And, of course, if they are attacking with shortbows, they don't benefit from their shield's AC bonus!
Setting is hot and dry badlands on a dangerous trail to the frontier town of Fandango. The oxen and wagon treat anything off the trail as difficult terrain and cannot move over the dead horses. Dry brush - quite flammable, actually - offers half cover for any Medium-sized or smaller creature standing in it (2 x 2 squares). For other details, see the Starter Set.
* Late edition: If either Auroch or Bullock are killed, the remaining ox will not pull the wagon.
Even if you don't re-theme the adventure as I have, consider using this way of approaching the encounter. I think it will make for a much more dynamic scene than a straight-up ranged/melee battle, possibly providing greater impetus for the PCs to follow the goblin trail to recover stolen wares. At the end of the scene, calculate how much value was stolen or destroyed and see how far in arrears this puts the characters - that's just more motivation to get to earnin'!
How would you handle this scene if you were a PC? How about as DM? What constructive feedback do you have to improve this scene?
Good luck and have fun, pardners!