Place the onion, celery and green pepper into a blender. Pulse until chopped, but not quite pureed. Squeeze out any excess moisture. It is important to get as much moisture out as you can. I put the vegetable mixture in a cheesecloth and wrung them like a wet towel.
Place beef and pork into a large bowl. Add onion mixture.
Whisk egg with milk and add to beef mixture, along with the bread crumbs and steak seasoning.
In a separate bowl, combine the barbecue sauce, salsa, and Worcestershire sauce. Pour half of the sauce onto the meat mixture and combine all ingredients well. Reserve the remaining sauce.
Spray a 9x13 aluminum (or glass if using the oven) pan with non-stick spray.
Add the beef/pork mixture and form into a roll. Spoon remaining sauce over top.
If cooking in the oven, bake 45-60 minutes or until center is done. You may want to drain some of the accumulating fat before serving.
If cooking in the smoker, poke a few holes along the edges of the aluminum pan so that any accumulating fat drips out. Smoke 2-3 hours at 250 F or until the center is done.
Let meatloaf rest for 10 minutes and then slice into thick pieces.