Prep the avocados - Cut the avocados in half, remove the pit, and scoop out the flesh. Add to a bowl, chop roughly, and then smash with a fork. Squeeze the lime juice into the bowl and stir to combine.
Mince the onion and pepper - Peel the onion and mince it. Destem, deseed, and mince the jalapeño. Add to the bowl with the avocado.
Finish - Stir in the cumin and salt, to taste. Cover with plastic wrap, placing it directly onto the guacamole so that it's not exposed to the air. Store in the fridge until ready to serve.