Take Jalapeno and set on cutting board to find its stable point to insure that it won't roll during cooking and make your slice there. Slice form the base of the stem to the tip.
Once you have finished with all of your slices then core or de-seed your Jalapenos. The method that I use is to use a Perry Knife. with the Pepper on the counter I would with my thumb on the Jalapeno tip and my index finger on the top near the stem give a gentle squeeze and the slit will open up just enough to gently slice the white inards and de-seed the Pepper. Then running under water to get the last remaining seeds.
Now that you have a big bowl of sliced, de-seeded Jalapenos cook and rinse your shrimp or sausage and let cool to room temp. Once you have that then put just enough in each Pepper so that uo can get a good amout of cheese inside.
Now grate your cheese and finely chop your cilatro and blend together.
I like cilantro so I use a good amount but you can use at your discretion and same goes with the Onion.
When stuffing your Peppers with cheese remember to stuff them full but try not to over stuff them so you can't get the slit closed or all most closed.
Put your stuffed Jalapenos in a Pirex baking dish side by side with slit up and cover until cooking time.
Take out of fridge at least an hour before you bake.
Bake at 400 for 20 minutes the boost it to 425 for 5 more minutes the take out and let rest for at least 15-20 mins.