Make the salsa: Heat the vegetable oil in a heavy saucepan over medium-high heat. Add the garlic, onion and 1/2 teaspoon salt and cook, stirring, until the onion is translucent, about 4 minutes. Add the chiles, tomato, 2 cups water and the bay leaf. Bring to a boil, then reduce the heat to medium; simmer until the chiles are soft and tender, about 20 minutes. Remove from the heat and let cool slightly.
Remove the bay leaf, then transfer the vegetables and about 1 cup cooking liquid to a blender and puree until smooth, adding more cooking liquid if necessary. Strain through a fine-mesh sieve back into the pan; cook until slightly reduced, about 10 minutes. Set aside.
Make the tacos: Heat the vegetable oil in a large heavy saute pan (do not use a nonstick pan) over medium-high heat. Add the potato and saute until golden, 8 to 10 minutes; transfer to a bowl. Add the pork to the pan, season with pepper and sear until browned, about 3 minutes per side. Add the broth and bring to a simmer. Add 1 cup of the prepared salsa and return the potato to the pan; cover and simmer until the pork is fork-tender, 50 minutes to 1 hour. Serve in tortillas; top with more salsa, cilantro, onion and radishes.