Start by bringing a large pot of water to a rolling boil. Here’s where you’ll be adding the first hints of flavor. Toss in a generous pinch of salt along with the baking soda. Now, don’t be alarmed if the water froths a bit; that's totally normal. The baking soda helps the greenery stay bright while cooking. Once it’s boiling, add the amaranth greens and let them cook for about 2 minutes. After that, drain them in a colander and set them aside—let’s keep that vibrant green color intact!

In a large cazuela or any sturdy pot over medium-high heat, drizzle in the olive oil. When it’s hot and shimmering, add the pieces of pork loin. Sprinkle in some salt while the meat browns to build flavor. Let it sizzle away, turning occasionally so it cooks evenly. After about 5 minutes, when the pork is nice and browned, it’s time to add the sliced onion and diced peppers. Cook this mixture for another 5 to 7 minutes, or until the vegetables soften up and hang out with the meat.

Now, for the fun part! Stir in the minced garlic, letting it cook for another minute or so until it’s aromatic—your kitchen will start to smell incredible. Following that, sprinkle in the cumin powder and dried oregano for an extra kick of flavor. Toss in the nicely chopped tomatillos and pour in the stock or water. Give everything a good stir and bring the mixture to a gentle simmer.

Allow your dish to simmer for about 15 to 20 minutes. This is when the magic happens—the pork becomes tender and soaks up all those tasty juices while the liquid cooks down. Don’t hesitate to add a bit more salt to get the flavors just right.

Once the pork is tender, fold in the amaranth greens and chopped cilantro. Mix everything well and let it cook for another 5 minutes. This step melds all the flavors together, making the dish harmonize as a single entity. When you’re ready to serve, don’t forget to garnish with some toasted pepitas or sunflower seeds for that delightful crunch!