Place a medium sauté pan over medium-high heat and let it warm before adding the aromatics. A hot pan helps the onion begin cooking as soon as it touches the oil.

Add the olive oil, onion, garlic, and a pinch of salt, then cook until softened and lightly browned before taking the pan off the heat to cool completely. The onion should look tender with pale golden edges rather than dark, crisp patches.

Mix the beef, cheese, optional chilis, salt, cumin, oregano, and pepper in a bowl, then work in the cooled onion and garlic. The cheese and seasonings should run evenly through the filling without large clumps of plain beef.

Align all six tortillas and use a serrated bread knife to shave away the curved edges on four sides, saving the trimmings if desired. Use gentle back-and-forth strokes to create a square while removing as little tortilla as possible.

Separate the filling into five similar portions, spread each portion over a tortilla square, and assemble the filled tortillas with the sixth, unfilled square on top. Thin, even coverage keeps the slab level and avoids bulky pockets that can push the layers apart.

Compress the assembled slab firmly and use a spatula to tuck escaped filling back along the edges. The sides should look compact, with the top tortilla sitting flat rather than bowing over mounds of meat.

Cut six equal strips, turn each onto its side with the layered cross sections facing upward, align them parallel, push six evenly spaced skewers across all the strips, and cut between the skewers. Each finished skewer should hold a row of layered pieces, with the stick passing through every strip rather than running along a tortilla seam.

Warm the vegetable oil in a large cast iron or nonstick skillet over medium heat, then cook the skewers for 2 to 3 minutes on each of their four sides. Turn when the surfaces develop a golden crust and sizzling cheese edges, and continue cooking as needed until the beef in the center reaches 160°F on an instant-read thermometer.