Preheat oven to 400 degrees F, and prepare a baking sheet by lining with parchment paper - set aside.
Wash and thoroughly dry your cremini mushrooms, then spread out on the parchment lined baking sheet and sprinkle with salt & pepper.
Combine the jalapeno, onion, garlic, 1/4 C. cornmeal, 1/4 C. butter, and optional kielbasa in your food processor, along with 1/2 of the cremini stems.
Pulse a few times, until the ingredients are combined - not too much so that they puree. Two or three pulses should be sufficient.
Stuff the cremini caps with your butter mixture. Sprinkle 1/4 C. parmesan cheese over the stuffed mushroom caps, then sprinkle with remaining 2 Tbsp cornmeal.
Bake at 400 degrees F. for 15-20 minutes, or until mushrooms have given up their juices.
If needed, broil for a minute or two to crisp up - as needed.