Bring a large pot of salted water to a rolling boil for the fusilli. Use 1 liter of water per 100 g of pasta as a guideline so the gluten-free pasta has plenty of room—this prevents sticking and helps the pasta cook evenly. Salt the water well (it should taste like the sea) so the pasta is seasoned from the inside.

While the water is heating, dry-toast the pumpkin seeds in a small skillet over medium heat for 3–4 minutes, shaking the pan constantly until they are fragrant and just beginning to color. Toasting concentrates flavor and adds nuttiness and crunch that contrast the tender pasta and saucy beef. Transfer to a bowl to stop them from continuing to cook.

Heat 2 tablespoons of olive oil in a large heavy skillet or sauté pan over medium-high heat. If using onion and garlic, add the chopped onion and a pinch of salt and sweat for 4–5 minutes until soft and translucent—this builds savory sweetness. Add the minced garlic for the last 30 seconds to 1 minute to release aromatic oils without burning.

Add the ground beef in a single layer and let it sit undisturbed for 1–2 minutes to develop a fond (browned bits) — browning adds deep, savory flavor. Break the meat up with a spatula into bite-sized pieces and continue to cook until nicely browned and no longer pink, about 4–6 minutes total. Season lightly with salt and a few grinds of black pepper while cooking so the seasoning distributes through the meat.

When the beef is browned, pour in the roasted tomatillo sauce (560 ml). Increase the heat to bring the sauce to a simmer, then lower to medium-low. Simmer gently for 6–8 minutes so the flavors meld and the sauce reduces slightly—this concentrates the tomatillo and chipotle flavors and helps the sauce cling to the pasta. Taste and adjust salt and pepper.

Add 1 tablespoon of fresh lime juice to the sauce while it simmers to brighten the overall flavor and lift the smoky chipotle. Reserve the remaining lime juice for finishing. Stir in half the chopped oregano (2 tsp) toward the end of the simmer so its leaf oils remain vibrant without becoming bitter from prolonged cooking.

When the pasta water reaches a boil, add the gluten-free fusilli and cook according to package directions minus 30 seconds to 1 minute for al dente—gluten-free pastas can go from perfectly chewy to mushy quickly, so slightly undercooking ensures a firm bite once finished in the sauce. Reserve 1 cup (240 ml) of pasta cooking water before draining.

Drain the pasta and add it straight into the skillet with the simmering chipotle beef and tomatillo sauce. Toss over low heat, adding splashes of the reserved pasta water as needed to loosen the sauce and help it emulsify with the meat and olive oil—this technique makes a silkier, better-clinging sauce. Cook together 1–2 minutes so the pasta finishes cooking in the sauce and absorbs flavor.

Turn off the heat and stir in the remaining 2 tablespoons of olive oil and the remaining lime juice to add gloss and a fresh citrus lift; the oil helps coat the pasta while the lime cuts through richness. Taste and adjust salt, pepper, and lime according to preference.

Plate the pasta into warm bowls. Sprinkle the toasted pumpkin seeds generously over each portion for crunch, and finish with the remaining chopped oregano for herbal brightness. If desired, add a final drizzle of extra-virgin olive oil and an extra squeeze of lime.

Serve immediately so the toasted seeds stay crunchy and the pasta remains al dente. Leftovers will thicken as the pasta absorbs sauce; gently reheat with a splash of water or stock to loosen.