Preheat oven to 350ºF.  Coat a 10x15-inch jelly roll pan with nonstick cooking spray or brush with 1 tsp canola oil and line it with parchment paper.  Pro Tip: gently scrunch the parchment into a ball, and then smooth it out again.  Doing this will allow the parchment to lay flatter and sit nicer in the creases and corners of the pan.  Allow an overhang of 1 inch on all sides, and lightly spray or brush the top of the parchment paper with oil (1 tsp would be sufficient). Set aside.

In a skillet over medium heat, add remaining 2 tsp canola oil and sauté onions until just starting to soften, then add the peppers.  Sauté for 1-2 minutes, or until desired doneness of veggies.  I prefer a little crispness to my peppers, so I don’t tend to cook them too long.  Remove from heat and allow to cool slightly.

Place the flour in a small bowl and slowly pour the milk over the flour in a steady stream. Whisk until smooth and ensure there are no lumps.

In a medium bowl, whisk together the eggs, mustard, soy sauce, and pepper. Add the milk mixture and whisk for about 2-3 minutes, or until it has some medium to large sized bubbles. Pour the mixture into the prepared sheet and evenly sprinkle with the sautéed onions and peppers, chopped kielbasa and 1/2 cup of the cheese over the top.

Bake for about 12 minutes, until the edges are set and the center is beginning to set (it will still be a little wobbly). Remove from the oven, sprinkle 1 cup of cheese on top, and bake for another 5 to 6 minutes, until the cheese is just melted and the center has set. Remove the pan from the oven and let cool for about 5 minutes.

Once the omelet and pan have cooled slightly, gently lift the long end of the parchment paper and tightly roll the omelet to create a long cylinder. Sprinkle with the remaining 1/2 cup cheese and the green onions.

Slice and serve warm.