Preheat the oven to 350°F. Brush 2 tablespoons of canola oil onto the inside bottom and sides of a 13×18-inch rimmed baking sheet. Set aside a second rimmed sheet tray for later.
In a large skillet over medium-high heat, heat 1 tablespoon of canola oil. Sauté the chopped onions for 2-3 minutes until translucent. Remove and set aside.
In the same skillet, cook half the ground beef with 1 packet of taco seasoning, 1 tsp salt, and ½ tsp black pepper, breaking up the beef until fully cooked. Transfer to a bowl and repeat with the second batch of beef.
Mix the cooked onions with the ground beef in the bowl.
Lay 10 tortillas over the prepared sheet pan, letting them overhang by 2-3 inches. Ensure there are no gaps between the tortillas.
Spoon the ground beef mixture evenly over the tortillas, allowing the fat to drain before placing the meat.
Sprinkle shredded cheese over the beef, followed by pico de gallo (drained of excess liquid).
Place the remaining 6 tortillas on top, overlapping in the center. Fold the overhanging tortillas over the top.
Brush the top tortillas with 2 tbsp of canola oil. Place the second sheet tray on top and weigh it down with an oven-safe skillet. Bake for 30 minutes.
Remove the skillet and top tray, then bake for an additional 30 minutes until golden and crisp.
Let the tacos rest for 5-10 minutes before slicing and serving. Garnish with sour cream and pico de gallo.