Preheat oven to 400°. In a large frying pan over medium-high heat, brown steak and chorizo, stirring, about 5 minutes. Meanwhile, chop onion and mince garlic. Add onion and all but 1/8 tsp. cumin to pan. Stir often until onion is soft, 4 to 5 minutes. Reduce heat to medium; stir in 1 1/2 cups salsa. Simmer until thick, 8 to 10 minutes, stirring occasionally.
While steak mixture simmers, combine black beans, 3/4 cup water, oregano, 1 tsp. garlic, and chiles in a small saucepan. Bring to a boil over high heat, then reduce heat to medium and simmer until all but about 1/4 cup liquid has evaporated, 10 minutes.
Meanwhile, make guacamole: Pit and peel avocado. In a bowl, mash avocado with remaining 1 tbsp. salsa, remaining 1/8 tsp. cumin, remaining garlic, and the lime juice. Stir 1 tbsp. cilantro into guacamole and add salt to taste.
Line a large, rimmed baking pan with parchment paper. Arrange chips in a 12-in.-wide circle. Sprinkle with cheese. Bake until cheese melts, 3 to 4 minutes.
While chips are baking, arrange lettuce around rim of a large serving platter (at least 16 in. wide). With a wide spatula, loosen chips from parchment. Carefully lift parchment from pan, then slide chips off paper into center of platter. Spoon meat mixture over chips. With a slotted spoon, top with beans. Spoon guacamole over center of nachos and sprinkle with remaining 1 tbsp. cilantro.
This was my first time making nachos and they turned out delicious. I have just a few tips. First, the timing in the recipe is totally off. You need to start making the bean mixture while the onions are cooking, and count on the meat mixture to take about 5 minutes longer than it says to reduce enough. Second, I'd recommend you try chihuahua cheese instead of jack if at all possible - and apply liberally! It's the best cheese for nachos. Third, add in a can of diced tomatoes with the chile verde. You won't regret it. :) Happy cooking!