Heat canola oil in large skillet over-medium high heat. Season pork with salt and add to skillet. Cook for 15 minutes and then flip and cook for another 10 minutes, or until cooked through and golden brown.
Add the pork, onion, tomato sauce and pepper and pulse until a thick paste forms. Set aside.
Using a stand mixer fitted with the paddle attachment, beat the masa flour, salt and water on medium speed until the dough is thick and sticky. Let rest for 15 minutes.
Add 1 cup water and 2 tablespoon oil to a small bowl and wet your hands so the dough won't stick to them.
Take a golf ball-sized portion of dough and roll into a ball. Flatten into a disc about 4 inches in diameter. Fill the dough with 1 tablespoon of the pork and ½ teaspoon of cheese. Fold the dough over the filling so it is completely sealed.
Working gently, press the dough into a flattened disc about 4 inches in diameter. If the pupusa cracks, just patch it with some dough. Repeat with the remaining dough and filling.
Heat a large skillet over medium heat and brush with some canola oil. Add 3 pupupas to the skillet and cook for 3-4 minutes, or until golden brown and then flip and cook another 3-4 minutes or until golden brown. Repeat with remaining pupusas.
Make sure you cook the pork over medium-high heat to get a nice char which is added flavor.
If you like more heat, leave some of the seeds from the jalapeño in the filling.
Wet your hands with some water and oil as you are shaping the dough so it doesn't stick.
If the pupusa dough cracks, just patch it with some extra dough.