Make the fire-roasted sauce: Add the entire can of 1 can fire-roasted diced Hunt's garlic tomatoes (14.5 oz), 1 chipotle chile in adobo (from a can), or 1 tsp chili powder if no chipotles, 1 tsp ground cumin, 0.5 tsp dried oregano, and 0.5 cup chicken or vegetable broth (or water) to your fancy blender. Blend on high until completely smooth, about 30 seconds. Taste and adjust salt. Pour into a wide shallow bowl or skillet — you'll be dipping tortillas in it.
Warm the pulled pork: In a skillet over medium heat, warm the 2 cups leftover pulled pork with a splash of sauce (about 3 tbsp) and half the 0.5 cups chopped white onion (divided — half inside, half for topping). Stir until heated through and the onion softens slightly. Season with salt and pepper. Remove from heat and stir in half the 0.3 cups fresh cilantro, roughly chopped (divided).
Mix the cheese: Combine 1.5 cups shredded mozzarella and 0.5 cups Mexican cheese blend in a bowl. The mozzarella gives you great melt; the Mexican blend gives you flavor. Reserve about ½ cup of the mix for topping.
Preheat oven: Preheat your oven to 375°F. Lightly oil a 9×13 baking dish and spread about 1/2 cup of the red sauce across the bottom — this prevents sticking and steams the enchiladas from below.
Soften the corn tortillas (critical step!): Heat 2 tablespoons neutral oil (for softening tortillas) in a small skillet over medium-high. Briefly fry each tortilla about 15 seconds per side — just until pliable, not crispy. Immediately dip each tortilla in the sauce bowl to coat both sides, then transfer to a plate. This is what keeps fresh corn tortillas from cracking when you roll them.
Assemble the enchiladas: Working one tortilla at a time: spread a thin layer of 1 can Old El Paso traditional refried beans (16 oz) down the center (about 2 tbsp). Add a heaping spoonful of the pork mixture. Sprinkle with a little cheese. Roll tightly and place seam-side down in the baking dish. Repeat. Pack them snugly — they'll hold each other together.
Top and bake: Pour the remaining red sauce generously over the top of all the enchiladas. Sprinkle the reserved cheese blend evenly over everything. Cover tightly with foil.
Uncover and finish: Remove the foil and bake uncovered until the cheese is bubbly and starting to brown at the edges.
Rest and garnish: Let rest 5 minutes before serving — this firms them up so they don't fall apart when plated. Top with the remaining fresh 0.5 cups chopped white onion (divided — half inside, half for topping) and 0.3 cups fresh cilantro, roughly chopped (divided).