Heat the oil in a large skillet over medium heat. Season the pork with salt and pepper. Add the pork to skillet and stir to coat with oil. Place the jalapeno peppers into the pan and cover; allow to simmer 20 minutes. Uncover and remove the jalapenos from the pan; chop roughly and set aside. Continue cooking the pork, uncovered, until it browns completely and the liquid evaporates, about 10 minutes.
Mix in the onion and garlic; cook and stir about 2 minutes. Add the mushrooms and cook 1 minute more. Pour the tomatoes and chopped jalapenos into the pan and stir through the pork. Season with the cumin. Stir, cover, and reduce heat to low; simmer another 10 minutes.
