Heat the olive oil in a Dutch oven or heavy saucepan over medium-high heat. Add the cubed pork, garlic, onion, cumin and oregano. Cook and stir until pork is browned.
Cook and stir for a few more minutes, then pour in the vegetable broth. Reduce the heat to low, and simmer for about 30 minutes.
Add the potato to the stew, and simmer for about 45 minutes. You can roast your chilies during this time, peel, seed chop and add to the stew along with the serrano peppers. If the stew becomes too dry, add a little water. When the potatoes are soft and the pork is tender, add the tomatoes. Cook for about 10 minutes, then remove from the heat and serve.